Antibody Diversity is Genetically Determined

Immunoglobulins are molecules providing immunity and protection from infections and microbial attacks. They have a typical Y shape. That is the reason they catch hold of microbes such as bacteria and viruses. 

The unique molecule of the microbes is known as an antigen. The antibody's Y structure has a region known as a paratope. It binds with the epitope of the antigen. Then it makes the process of elimination easier. Antibodies have a variety of functions. It is important to judge the greatness of an antibody based on its biological effect on a pathogen or the toxins produced by a pathogen. It is an important hallmark for many lab tests that an antibody binds to a particular antigen. Studying and knowing about antibodies is key to developing potential vaccines and therapeutics. Functions of the antibodies, such as virus neutralization, may help to inhibit pathogenesis.

The inhibitory results of antibodies on pathogenic organisms were recorded since the 1800s. Since then, many things have been known concerning the means that underlie the anti-microbial action of antibodies. However, these Y-shaped molecules often have numerous functions in vitro and in vivo. They either involve direct means or via interactions with FcRs or compliments. 

Modern means, such as knockout mice or antibodies engineered to repeal or improve functions have demonstrated promising results for more accurate investigations of antibody function. Yet, major questions about how an antibody plays roles in vivo remain unanswered, and multiple actions are possible to contribute to the anti-microbial influence.

The complexity of our immune system mainly depends on the immune cells such as the B cells, T cells, various antibodies, and other cells. As soon as a foreign molecule or a microbe enters the body, our immune system gets activated. The soldiers of the immune system, mainly the immune cells and the antibodies come forward and activate a cascade of mechanisms involved in killing the foreign particles and the microbes. They not only eliminate the microbe from the body but also remember it as an enemy so that when the same microbe re-enters next time, they easily eliminate it. The antibodies usually denoted as Y-shaped molecules, bind to the antigens and help in eliminating them. The antibodies exhibit diverse nature and their synthesis completely depends on certain gene expressions. These antibodies show receptors specific to the antigens. Although there are few genes in the human body, the antibodies have very diverse receptors. Hence, they identify many different types of antigens.

While distinguishing or recognizing foreign substances, our immune cells do not get confused with the cells inside the body. Hence, they differentiate the foreign cells and their own cells cleverly. The phenomenon of identifying a foreign antigen is known as immune recognition. Antibody structures exhibit complexity. Thus, they recognize a wide array of foreign antigens. Sequencing data reveals a specific amino acid sequence in the variable region and a few invariant sequences in the constant regions. Determination of an antibody involves specificity and sensitivity. The property of the antibody of being specific helps to determine the homologous and heterologous epitopes. The sensitive property of an antibody helps to recognize the antigen in between thousands of other substances. It is important to study the antibody structure before studying the diversity.

Image 1: Antibody diversity

Antibody (Immunoglobulin structure):

Antibodies are Y-shaped glycoproteins with four main polypeptide chains. The two long polypeptide chains with many amino acids are known as heavy chains. The remaining two chains consisting of short polypeptides are known as light chains. Each light chain gets connected to a heavy chain through a disulfide bond. The heavy and the light chains mainly consist of two distinct regions. The tips of heavy and light chains consist of the variable region (V). The remaining is known as a constant region (C). The variable region attaches to the antigen. A normal human being consists of one million antibodies with different antigen-binding specificities. Hence, the variable region consists of different amino acid sequences. Five types of heavy chains include γ, α, ε, δ, and μ. Two types of light chains are known as κ and λ. Types of antibodies in humans include IgA, IgD, IgE, IgG, and IgM respectively. 

Antibody diversity and Genetics:

A separate set of multigene families encode for heavy and light chains situated on different chromosomes. The light chain genes are present on the 2^nd and 22^nd chromosomes. The heavy chain genes are present on the 14^th chromosome. Several coding sequences known as gene segments get separated by the non-coding segments. On maturation of the B-cells, these genes get rearranged, thereby forming a functional immunoglobulin. Restriction mapping is a kind of physical mapping that shows specific sites for the restriction enzymes. They involve separation by lengths and are marked in numbers by bases. Hence, the study of DNA segments encoding the antibodies involves a restriction map.

The DNA segments encoding a variable region get separated from the DNA segment encoding a constant region by an intermediate region encoding a joining segment. The heavy chain studies revealed the presence of one more region known as the D region (for diversity) placed between the V and J regions. A non-coding region separates each of the coding regions. A single type of gene gets expressed for each V, D, J, and C region in a single antibody molecule. Various DNA coding regions naturally recombine to produce a diverse antibody. 

Image 2: Antibody structure

Various regions	Total Genes	The number of genes expressed
Variable region (V)	86	1
Diversity region (D)	30	1
Joining region (J)	9	1
Constant region (C)	11	1

Table: The expression of the genes in various regions

Splicing and recombination:

Naturally, DNA recombination occurs in the coding segments. For forming a heavy chain, splicing of any one variable region on a D region occurs followed by a J region. This process of splicing is known as V-D-J joining. Then the constant portion of the heavy chain undergoes splicing. The transcription and translation processes follow these events. RNA processing involves the splicing of the introns or the non-coding regions. When the antigen stimulates an immune response, the heavy chain DNA undergoes a further rearrangement in which V, D, and J combine with any C gene segment. The V, D, J, and C regions for a heavy chain DNA are known as V_H, D_H, J_H, and C_H respectively. The process is known as class switching. Exactly how the process occurs remains unclear. However, there are flanking regions situated upstream of the C_H region consisting of multiple copies of short repeats (GAGTC and TGGGG). Mutations also help to increase the genetic variation of the antibodies.

Image 3: V-D-J rearrangement

Antibody diversity differs in various species:

The creation of most of the immunoglobulin genes is similar in humans and mice. There is a combinatorial repertoire of immunoglobulin genes. The combinatorial rearrangements of VDJ gene segments are germ-line based.   It occurs primarily in the bone marrow. In organisms such as birds, rabbits, sheep, cattle, and others, the primary repertoire gets generated in the gut-associated lymphoid tissue (GALT). Many species do not undergo combinatorial VDJ rearrangements. Chickens involve a limited repertoire of functional VDJ genes. Hence, the B cells migrate to the Bursa of Fabricius and undergo rapid proliferation and diversification mediated by gene conversion. In rabbits, gene conversion and somatic hypermutation occur in the GALT in the specialized microenvironments of the appendix. The sheep and the cattle diversify their antibodies in the Peyer’s patch. The jawed vertebrates including the cartilaginous fish undergo VDJ rearrangements. Jawless fish such as Hagfish and Lampreys lack adaptive immunity. These fish use completely different genes known as variable lymphocyte receptors (VLRs) to generate an immune response. These VLRs are leucine-rich repeats capable of producing somatic diversity. Not only animals and fish but also plants and insects possess immunoglobulin genes.

Gene conversion is not an ordinary process. It extensively diversifies the rearranged genes. Gene conversion is a special case of somatic mutation, thereby known as somatic hypermutation. The word somatic hypermutation indicates the occurrence of a high-class mutation in the variable regions of the immunoglobulin genes. Thus the gene sequence portions get modified assuming the corresponding sequence of the donor gene. The donor gene acts as a template gene. This type of somatic mutation is known as templated somatic mutation. Once the antigen enters the immune system, it gets exposed to millions of antibodies. But only a few types of antibodies have a sufficient affinity to trigger an immune response. Depending on the affinity binding, antibodies with sufficient affinity interact with the antigen.

AgDscam genes in mosquitoes:

Insects such as mosquitoes possess genes encoding immunoglobulins. However, they lack specific mechanisms such as somatic hypermutation and recombination. Hence, mosquitoes have a different mechanism. The researchers at John Hopkins discovered AgDscam, a way in which mosquitoes combine their immunoglobulin domains of a single gene. AgDscam indicates Anopheles gambiae Down’s syndrome cell adhesion molecule. It produces a variety of pathogen-binding proteins. It follows the process of alternative splicing guided by immune signal transduction pathways. Hence, it helps to increase the binding capacity of various pathogen binders.

Thus, in conclusion, antibody diversity occurs through gene recombination. The process of gene recombination varies from organism to organism. Humans involve enzyme-mediated VDJ recombination, gene conversion, and somatic hypermutation. The other organisms may involve slightly different mechanisms. Hence, these genes play an important role in building the immune system.
References:

[1] Kuby Immunology

[2] Immunology, Pathak, and Palan

[3] Genetics, 9th Edition (Multicolour Edition), Verma P.S. & Agarwal V.K.

[4] Principles of genetics, 8th ed, Gardner, M. J. Simmons, D. P. Snustad
[5] Insect Infection and Immunity: Evolution, Ecology, and Mechanisms, Jens Rolff, Stuart Reynolds

© Copyright, 2018 All Rights Reserved.

Gene mapping in eukaryotes

Mapping the genes in a correct order helps to know the location of the genes on the chromosomes. Various techniques achieved success in mapping the genes. Mapping techniques achieved success with eukaryotic organisms such as Drosophila and plants before humans. Gene mapping not only helps us in knowing the exact location of the gene but also helps in conducting various other experiments based on the gene location. Thomas Morgan worked with Drosophila strains and found out recombination mechanisms. An experiment sometimes gives an idea of other hidden strategies. For example, gene mapping studies revealed the mechanism of recombination. The studies revealed that the progeny obtained by crossing some strains of the eukaryotic organisms also showed phenotype differing from the parental phenotype.

Morgan’s experiment:

Thomas Morgan and his colleagues worked with Drosophila strains. They cultured Drosophila with a particular X-linked phenotype. The experimenters selected certain strains of fruit flies. The female flies had two X chromosomes with linked genes. The males had one X and one Y chromosome. The female flies had a phenotype of white eyes and miniature wings. The male flies were wild-type flies. The cross between these two types of flies gave rise to an F1 generation having wild-type females, and white-eyed, miniature winged male flies. Interbreeding of the F1 progeny gave different kinds of flies. There were total 2241 flies in the F2 generation. Out of these, total 900 flies had a non-parental phenotypic combination of white eyes and normal wings. Other types of non-parental strains included red-eyed, miniature winged flies. The non-parental ones are known as recombinants. The recombinants arise due to the crossing over between the homologous chromosomes. The theory involves two key concepts. The first one is the site of physical exchange. It is known as the chiasma. The second one involves the genetic recombination between the linked genes. It is known as crossing over. It also involves a reciprocal exchange of chromosome segments.

Image 2: Morgan's experiment

Stern’s Experiment:

Stern worked with X-linked gene loci in Drosophila. The experimenters conducted a cross between the wild-type bar eyed females and carnation type round-eyed males. The female flies had two X chromosomes. One of them additionally had a detached piece of X chromosome. The other X chromosome had an additional attachment of a piece of the Y chromosome. The chromosomes in the males flies had no extra pieces attached. The interbreeding of the F1 progeny gave rise to different types of flies. Four main types of progeny observed included carnation bar, red round, carnation round, and red bar eyed males and females respectively. The results of the experiment revealed the genetic recombination and exchange of identifiable segments. 

Barbara McClintock’s corn experiment:

The corn species selected for the experiment consisted of heterozygotes for the two genes on the 9^th chromosome. One of the genes gave a phenotype of colored versus colorless. The other type of genes resulted in the phenotypes such as standard type starch with amylose and amylopectin versus waxy plants having the only amylopectin. The chromosomes had genes cWx giving normal phenotype. The homologs of the chromosomes having genes cWx had the genotype of Cwx. These homologs had a large double stained knob and a piece of 8^th chromosome attached near the wx gene. It was a translocated segment. These features are known as the cytological markers. Hence, the corn experiments revealed the process of genetic recombination associated with the physical exchange between the parts of the homologous chromosomes.

Linkage studies using testcross:

A cross involving a normal individual with an individual who is homozygous recessive for all the genes is known as a testcross.

·        Two point test cross

Consider the autosomal recessive individuals. Suppose there involves a cross between the double heterozygotes with a genotype of a⁺b⁺/ a⁺b⁺ and double homozygous recessives with a genotype of ab/ab. The F1 generation revealed progeny with a wild-type a⁺b⁺/ab genotype. Upon conducting a testcross with double homozygous recessives, the progeny had 50% parental non-recombinants and 50% recombinant progeny. The formula for the recombination frequency involves (Number of recombinants/ Number of testcross progeny) x 100. The recombination frequency cannot exceed 50%.

Image 2: Two-point test cross

·        Three-point test cross:

Consider a cross between the triple heterozygotes with a genotype of a⁺b⁺c⁺/abc and triple homozygous recessives with a genotype of abc/abc. These crosses reveal the genetic recombination. Consider another example of flowering plants having three linked genes controlling the fruit phenotype. The recessive p allele gives a purple phenotype versus the wild-type yellow phenotype. The recessive r allele gives a round shape versus the wild-type elongated one. The recessive j allele gives juicy phenotype versus the wild-type dry fruit. The order of genes gets determined through a three-point test cross. Two parentals and six recombinants arise due to crossing over. The frequency of the double crossovers was found less than the frequency of the single crossovers.

Gene-centromere distance studies in Neurospora crassa:

The products of meiosis get a specialized arrangement depicting the four chromatids of each of the homologous pair of chromosomes. It usually reflects during the metaphase I. Neurospora consists of ordered tetrads. Meiotic and the mitotic divisions in the tetrads help in studying the process of recombination. It becomes easy to map the distance between the gene and the centromere using the ordered tetrads. The first division segregation tetrad consists of a parental type occupying half the ordered tetrad and another parental type in the other half of the tetrad. It occurs when there is no crossover. A single crossover between the gene and the centromere gives different types of tetrad segregation patterns (the second division segregation). The percentage of the second division tetrads divided by 2. It is known as the gene-centromere map distance. Tetrad analysis also helps in mapping two linked genes.

Mitotic recombination:

Crossing over is also known as genetic recombination between the linked genes or the reciprocal exchange of chromosome segments. It occurs during the mitosis as well as meiosis. The mitotic crossing over is also known as mitotic recombination. It leads to the production of the progeny cells having a combination of genes differing from the diploid parental cell entering the mitotic cycle. A classic example of the mitotic recombination includes fungus Aspergillus nidulans. It has a parasexual cycle of genetic systems. The genetic recombination in Aspergillus occurs through the processes other than regular alteration of meiosis and fertilization. The heterokaryon forms due to the mycelial fusion and the fusion of the two haploid nuclei. It gives rise to a diploid nucleus. The parasexual cycle also consists of mitotic crossing over within the diploid nucleus or haploidization of the diploid nuclei without meiosis. It becomes easy to calculate the gene order and the map distances.

Human gene mapping:

Physical mapping techniques help in mapping human genes. This technique mainly involves large genomes. It is not possible to set up a testcross for human genes since the human genome is vast. We obtain the recombination data from the pedigree analysis in humans. Gene mapping involves the use of gene markers and DNA markers.

                       
References:
[1] Genetics: Analysis of Genes and Genomes, Daniel L. Hartl, Elizabeth W. Jones
[2] Biology, Raven
[3] Biology, Pages 172-180, Neil A. Campbell, Jane B Reece
            

                                © Copyright, 2018 All Rights Reserved.

Recombinant DNA Technology

The aim of recombinant DNA technology involves cloning a specific gene. It is possible to produce multiple identical copies of a gene, a molecule, a cell through gene cloning. Recombinant DNA technology involves synergizing genetic material from different sources to create a new gene or a cell. Genetic engineering plays an important role in determining the structure of a gene, detecting carriers, diagnosing genetic disorders and gene therapy. Many hormones such as insulin, glucagon, and growth factors get synthesized using genetic engineering and used for commercial purposes. Before the advent of genetic engineering, there were limited sources for improvising crop quality, yield, agricultural techniques, and plant breeding.

However, with the recombinant DNA technology or genetic engineering, the yield and the crop quality started improving. Introduction of Stress and drought tolerance genes turned out to be successful. BT-Cotton is a classical example of recombinant DNA technology. It is a genetically modified crop involving resistance to bollworm infection. The plant gets modified with a specific gene helping the plant from bollworm attack. The gene product is a form of a protein. It gets released in the plant as soon as the worm attacks the plant. The worm immediately dies when it comes in contact with the gene product. Thus, BT-Cotton helped the farmers and the cotton industry grow. Many such success stories heard in the world involve the hard work of the recombinant DNA technologists. A body of techniques in recombinant DNA technology includes cutting the genes apart and splicing them with different pieces of DNA.

Image: Recombinant DNA technology

Materials used for recombinant DNA technology:

Recombinant DNA technology uses materials such as cells, bacteria, viruses, pieces of DNA, restriction digests, chromosomes, plasmid vectors, and many other substances. Commonly used organisms include bacteria as host organisms since they are single-celled structures. These bacteria are genetically engineered to produce vaccines, hormones, enzymes, and other biomolecules. For example, E. coli bacteria are genetically engineered to synthesize hormone insulin and growth factors. They also synthesize plant metabolites. An autonomously replicating DNA or a plasmid mostly depicts a circular, double-stranded DNA. Plasmids used in recombinant DNA technology replicate at each cell division. They are relatively convenient in isolation. Recombinant DNA technology allows the modification and manipulation of genes within or between the species. Hence, modification of plasmids involves restriction enzymes cleaving at a specific site and allowing foreign DNA inserts.

Recombinant DNA technology also utilizes viral vectors. However, it requires host genetic machinery for its replication.

Steps involved in recombinant DNA technology:

Cloning generates a series of DNA fragments. The first step involves cleaving the DNA segment at specific sites with the restriction enzymes. Restriction enzymes recognize and cut short sequences. They create a staggered or a blunt end in the DNA double helix. Now comes the role of a vector. A vector such as a virus or a plasmid carries a desired gene into the host and produces multiple copies.

Recombination:

Restriction enzymes cleave the DNA and produce either staggered or sticky ends. Thus, the plasmid DNA combines with foreign DNA. Their ends get sealed and stabilized through the action of another enzyme known as DNA ligase. The product obtained out of this activity is known as recombinant DNA. 

Transfer of the recombinant vector to the host:

The recombinant DNA molecules get introduced into the host organism. Once the recombinant plasmids get transformed into the host, they start multiplying themselves. The process develops identical foreign DNA molecules known as clones. A plasmid consists of genes showing resistance to antibiotics. The genes help the host to save themselves from the action of antibiotics. The absence of antibiotic resistance genes makes the bacteria sensitive to antibiotics. Screening of the clones involves nucleic acid hybridization.

References:
[1] Recombinant DNA Technology, Sardul Singh Sandhu
[2] Biotechnology-4: Including Recombinant DNA Technology, S. Mahesh

© Copyright, 2018 All Rights Reserved.

Bacterial conjugation process

The review article focuses on the plasmid-mediated conjugation process in E. coli bacteria. A unidirectional transfer of the genetic material through a contact between the two bacterial cells is known as conjugation. A physical bridge between the two cells mediates the DNA transfer. In prokaryotes, such as bacteria, the transfer of the genetic material mostly involves a one-way process. Thus, the process of conjugation helps to transfer the genetic material from one cell to another, enabling the process of copying the genetic material. Among the bacteria, most widely used ones for genetic analysis involve Escherichia coli bacteria. 
Lederberg and Tatum first conducted a conjugation experiment on E. coli cells. William Hayes demonstrated the theory of the unidirectional transfer of the genetic material in E. coli. Bernard Davis independently conducted a U-tube experiment. With the help of the above studies, various researchers came up with different findings in bacterial genetics. Conjugation studies also help to map the genes. In the late 1950’s, Francis Jacob and Elie Wollman studied the transfer of genetic material from Hfr strains to F^- strains. Most of the conjugation occurs through plasmids in the bacterial cells.

A plasmid is an extrachromosomal genetic material present in the bacterial cell. These plasmids exhibit a property of transferring the genetic material. Hence they are used as vectors in the process of cloning and recombinant DNA technology. The contact between the two cells involves a physical bridge between the two cells. Thus, a segment of the chromosome from one cell transfers to another cell thereby undergoing genetic recombination. Hence, the cells receiving the DNA are known as trans-conjugants. The essential genetic element for a bacterial conjugation is known as a conjugon. Unlike prokaryotes, the process of conjugation in protozoa involves a two-way process.

Image 1: Conjugation in bacteria

Lederberg and Tatum experiment:

Two E. coli strains to differ in their nutritious environments were studied. Note that even bacteria require nutrients for carrying out various cellular activities.  The two bacterial strains were labeled as strain A and strain B respectively. The amino acid synthesizing bacteria do not require a supplemented medium. Such type of bacteria labeled as “+” strains, synthesize the required nutrients. The strain A had a genotype known as met bio thr⁺ leu⁺thi⁺. The strain A bacteria grew on a medium supplemented with methionine and biotin. Without these two functional molecules, the strain A would not have grown. The strain B had met⁺bio⁺thr leu thi genotype. It required threonine, leucine, and thiamine to grow. Both the strains were mixed and plated on a minimal medium. The mixed culture gave rise to the prototrophic colonies. No colonies were visible on the minimal medium after plating the strains individually. It is due to the auxotrophic cells.

A mutant organism capable of growing only on a minimal medium with the growth factor supplementation not required by the wild-type strains is known as an auxotroph. A strain of microorganisms not requiring any additional nutrient to grow is known as a prototroph. The prototrophic colonies occurred at a frequency of 1 in 10 million cells. These colonies were recombinants arising due to the exchange of the genetic material between the two cells.

Davis U-tube experiment:

Bernard Davis showed physical contact between the two bacterial cells using a U-tube apparatus. He placed both the bacterial strains in a liquid medium poured into either side of the tube separated by a filter. The medium moved between the compartments. It was later on, plated on a minimal medium. None of the colonies grew. Hence, through this experiment, Davis demonstrated the cell to cell contact of the bacteria mediated gene transfer.

William Hayes experiment:

The genetic exchange in the E. coli occurred in one direction. One cell acted as a donor and the other like a recipient. Sex factor or the F factor-mediated the transfer of the genetic material. There are two types of bacterial cells such as the donor and the recipient cells. The donor cells are the one giving the genetic material. The recipient cells accept the genetic material from the donor cells. F-factor is a plasmid capable of replicating independently. Hence, the donor bacteria are known as F+ strains. The recipient bacteria are known as F- strains. Two same types of bacteria do not undergo conjugation. The F+ and F- strains only undergo conjugation.

F+ and F- matings:

The process of conjugation involves mating between F+ and F- strains. The F factor of the donor bacteria has a nick at one of the strands extending through the sex pilli or a physical bridge. The nicked strand gets transferred to the recipient where the remaining strand gets copied. Hence, the transfer and the synthesis of the DNA gets completed. Once the transfer of the genetic material from F+ to F- strains gets completed, the F- strain with the genetic material now becomes a donor or an F+ strain. It becomes a donor with a very high frequency.

Three types of plasmids based on their mobility include conjugative, mobilizable, and non-mobilizable plasmids. A protein gets involved in the conjugative machinery. It is known as relaxase. It is an important protein capable of recognizing the origin of transfer (OriT). The OriT is a short DNA sequence required in the cis position. Relaxase catalyzes the initial and final stages of conjugation. It resembles rolling circle replication proteins. The mobilizable plasmids thus carry OriT, relaxase gene, and nicking auxiliary proteins. Though conjugative and mobilizable plasmids appear similar in their properties, still they exhibit a difference in the machinery required for gene transfer.

Hfr strain:

The high-frequency recombination strains (Hfr) originate by rare crossovers. The Hfr strain arises due to the integration of the F factor into the bacterial chromosome. Such type of F factors is known as episomes. Hence, it replicates as a part of the bacterial chromosome. The Hfr cells conjugate with the F- strains. The nicked strands in the integrated factor F get transferred to the recipient F- strain, thereby transferring the bacterial genes. The transferred strand gets copied along with the genes. Recombination occurs in the recipient. Though the genes get copied, an F- strain never acquires Hfr phenotype because a complete copy of the F factor of the Hfr strain does not retain. Only a part of the F factor gets transferred.

Occasionally, the Hfr cell may not be efficient in excision of the F factor. The host chromosome adjacent to the F factor sometimes gets integrated into it due to an aberrant excision. Not only one but many segments get aberrantly inserted into it. During this excision, the F factor plus bacterial genes loop out of the chromosome. It leads to the formation of F’ factor. This type of conjugation is known as F-duction or sexduction.  

Image 2: Hfr strain

Bacterial gene mapping using conjugation:

The interrupted mating experiment helped in mapping the bacterial genes. It involved a cross between the F – and Hfr strains.

1.     Hfr strain had genes such as Hfr H thr⁺ leu⁺ azi^R ton^R lac⁺ gal⁺str^s

2.     The recipient had genes such as F^- thr leu azi^S ton^S lac gal str^R

“S” indicates sensitive and the “R” indicates resistant. The generation of the recombinants results from a double crossover. At various time intervals, the conjugating pairs broke apart and the transconjugants plated on a selective agar medium. It helped in studying the gene transfer. A single F factor gets integrated into Hfr strain. The interrupted mating experiment revealed the circular structure of the E. coli linkage map.

What is an inter-kingdom conjugation?

Nitrogen-fixing bacteria undergo an inter-kingdom conjugation. Agrobacterium tumefaciens and Agrobacterium rhizobium undergo inter-kingdom conjugation. A few pieces of evidence also report the inter-kingdom conjugation between the bacteria and the yeast. Hence, it is not necessary for the bacteria to undergo conjugation between their species. Inter-kingdom gene transfer is an example of horizontal gene transfer between two species, or different organisms.

Applications in genetic engineering:

The transfer of the genetic material through the process of conjugation involves convenience. It is possible to transfer genes from one bacterium to another, from bacteria to the yeast, plants or other cells. With conjugation, it is possible to use or synthesize a metabolite. Conjugative bacteria show the ability to pick up new plasmids from the environment. Recombinant DNA technology uses plasmids as cloning vectors. 

References:
[1] Int Std Ed-General Biology, Peter Russel
[2] Genetics of Bacteria, Sheela Srivastava
[3] Introduction to Genetics: A Molecular Approach, Terry Brown

© Copyright, 2018 All Rights Reserved.