Homologous Genetic Recombination during Bacterial Conjugation


Conjugation is the sexual transfer of deoxyribonucleic acid (DNA) from one bacterium directly into another. The transferred DNA can replace DNA of similar sequence in the recipient cell's chromosome by homologous genetic recombination, a process that both exchanges lengths of similar DNA sequences and repairs broken chromosomes, using similar chromosomes as templates.

Keywords: genetic exchange; horizontal gene transfer; sex; evolution; DNA double‐strand break‐repair; escherichia coli; RecA

Figure 1.

Conjugal transfer of DNA mediated by bacterial sex plasmids. (a) Transfer of extrachromosomal sex plasmid DNA such as F+ or F′ DNA. An F′ is illustrated with green F DNA and black DNA from the bacterial chromosome. Dashed lines represent newly synthesized DNA. Each line of the plasmid DNA represents a single DNA strand (polynucleotide chain). (b) Transfer of bacterial DNA of an Hfr strain, followed by homologous recombination of the transferred DNA into the recipient cell's chromosome. The usual folded and packaged (nucleoid) structure of the bacterial chromosome shown in (a) is not drawn in (b) for clarity in illustrating the recombination of Hfr DNA with the recipient chromosome (b). No real difference in chromosome structures is implied.

Figure 2.

General hypotheses for possible mechanisms of DNA recombination, as formulated by Meselson and Weigle. In this figure only, double‐stranded DNA is represented by helices. Newly synthesized DNA is symbolized by broken helices. (a) Break‐join models create recombined DNA from the parental DNA material. (b) Copy‐choice models form recombinant DNA without any material contribution of parental DNA, by switching the template for DNA replication from one molecule to another. To have no material contribution of parental DNA, the replication would have to be conservative (not the standard semiconservative segregation of DNA strands). (c) Break‐copy models use part of one parental DNA molecule to initiate DNA replication using another molecule as a template, joining the two by heteroduplex DNA.

Figure 3.

A model for a molecular mechanism of recombination of linear DNA in Escherichia coli, illustrated for conjugation. The model is synthesized (with modifications) from three sources (Rosenberg and Hastings, ; Harris et al., ; Razavy et al., ). Step‐by‐step description of this model appears in the text (Mechanisms Promoting Recombination). Each strand of duplex DNA is represented as a line. In single strands, arrowed ends represent 3′‐ends; nonarrowed ends represent 5′‐ends. Dashed lines represent newly synthesized DNA. The black DNA molecule represents linear DNA that will recombine with the (red) circular bacterial chromosome. SSB, single‐strand binding protein.

Figure 4.

Mismatch repair promotes the fidelity of DNA replication and recombination. (a) Mismatch repair proteins recognize incorrectly paired bases (shown) and 1–4 base insertion or deletion single‐strand loops (not shown) that result from DNA polymerase errors. Step by step discussion of this process appears in the text (Mechanisms Aborting Recombination). (b) Abortion of recombination between imperfectly identical DNA sequences by mismatch repair proteins. Mismatch repair proteins bind to mispairs (shown) and 1–4 base insertion/deletion loops (not shown) that result from heteroduplex DNA formation between homeologous DNAs during recombination, and impede recombination. The mechanism(s) by which mismatch repair proteins inhibit recombination after they have bound the mispairs in heteroduplex DNA is not yet understood (three downward arrows).



Clark AJ and Sandler SJ (1994) Homologous genetic recombination: the pieces begin to fall into place. Critical Reviews in Microbiology 20: 125–142.

Ellis NA (1997) DNA helicases in inherited human disorders. Current Opinion in Genetics and Development 7: 354–364.

Firth N, Ippen‐Ihler K and Skurray RA (1996) Structure and function of the F factor and mechanism of conjugation. In: Neidhardt FC et al. (eds) Escherichia coli and Salmonella Cellular and Molecular Biology, 2nd edn, pp. 2377–2401. Washington, DC: ASM Press.

Harris RS, Ross KJ and Rosenberg SM (1996) Opposing roles of the Holliday junction processing proteins of Escherichia coli in recombination‐dependent adaptive mutation. Genetics 142: 681–691.

Harris RS, Kong Q and Maizels N (1999) Somatic hypermutation and the three R's: repair, replication and recombination. Reviews in Mutation Research 436: 157–178.

Masters M (1996) Generalized transduction. In: Neidhardt FC et al. (eds) Escherichia coli and Salmonella Cellular and Molecular Biology, 2nd edn, pp. 2421–2441. Washington, DC: ASM Press.

Matic I, Rayssiguier C and Radman M (1995) Interspecies gene exchange in bacteria: the role of SOS and mismatch repair systems in evolution of species. Cell 80: 507–515.

Razavy H, Szigety SK and Rosenberg SM (1996) Evidence for both 3′ and 5′ single‐strand DNA ends in intermediates in Chi‐stimulated recombination in vivo. Genetics 142: 333–339.

Rosenberg SM (1997) Mutation for survival. Current Opinion in Genetics and Development 7: 829–834.

Rosenberg SM and Hastings PJ (1991) The split‐end model for homologous recombination at double‐strand breaks and at Chi. Biochimie 73: 385–397.

Further Reading

Hendrix RW, Roberts JW, Stahl FW and Weisberg RA (eds) (1983) Lambda II. Cold Spring Harbor, New York: Cold Spring Harbor Laboratory Press.

Kowalczykowski SC, Dixon DA, Eggleston AK, Lauder SD and Rehrauer WM (1994) Biochemistry of homologous recombination in Escherichia coli. Microbiological Reviews 58: 401–465.

Lloyd RG and Low KB (1996) Homologous recombination. In: Neidhardt EC, Curtis R III, Ingraham JL et al. (eds) Escherichia coli and Salmonella Cellular and Molecular Biology, 2nd edn: pp 2236–2255. Washington, DC: ASM Press.

Modrich P and Lahue R (1996) Mismatch repair in replication fidelity, genetic recombination, and cancer. Annual Review of Biochemistry 65: 101–133.

Myers RS and Stahl FW (1994) χ and RecBCD enzyme of Escherichia coli. Annual Review of Genetics 28: 49–70.

Neidhardt FC, Curtiss R III, Ingraham JL et al. (eds) (1996) Escherichia coli and Salmonella: Cellular and Molecular Biology, 2nd edn. Washington, DC: ASM Press.

Roca AI and Cox MM (1997) RecA protein: structure, function, and role in recombinational DNA repair. Progress in Nucleic Acid Research and Molecular Biology 56: 129–223.

Smith GR (1991) Conjugational recombination in E. coli: myths and mechanisms. Cell 64: 19–27.

Snyder L and Champness W (1997) Molecular Genetics of Bacteria. Washington, DC: ASM Press.

West SC (1994) The processing of recombination intermediates: mechanistic insights from studies of bacterial proteins. Cell 76: 9–15.

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Rosenberg, Susan M, and Motamedi, Mohammad R(Apr 2001) Homologous Genetic Recombination during Bacterial Conjugation. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0000581]