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The lambda red proteins promote efficient recombination between diverged sequences: implications for bacteriophage genome mosaicism.

Martinsohn JT, Radman M, Petit MA - PLoS Genet. (2008)

Bottom Line: However, the precise molecular processes underlying this mosaicism are unknown.To test this, we have measured the efficiency of homeologous recombination between diverged oxa gene pairs inserted into lambda.The recombination editing proteins, MutS and UvrD, showed only marginal effects on lambda recombination.

View Article: PubMed Central - PubMed

Affiliation: Faculté de Médecine R. Descartes, INSERM U571, Université Paris Descartes, Paris, France.

ABSTRACT
Genome mosaicism in temperate bacterial viruses (bacteriophages) is so great that it obscures their phylogeny at the genome level. However, the precise molecular processes underlying this mosaicism are unknown. Illegitimate recombination has been proposed, but homeologous recombination could also be at play. To test this, we have measured the efficiency of homeologous recombination between diverged oxa gene pairs inserted into lambda. High yields of recombinants between 22% diverged genes have been obtained when the virus Red Gam pathway was active, and 100 fold less when the host Escherichia coli RecABCD pathway was active. The recombination editing proteins, MutS and UvrD, showed only marginal effects on lambda recombination. Thus, escape from host editing contributes to the high proficiency of virus recombination. Moreover, our bioinformatics study suggests that homeologous recombination between similar lambdoid viruses has created part of their mosaicism. We therefore propose that the remarkable propensity of the lambda-encoded Red and Gam proteins to recombine diverged DNA is effectively contributing to mosaicism, and more generally, that a correlation may exist between virus genome mosaicism and the presence of Red/Gam-like systems.

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Recombination between the two homeologous oxa sequences flanking the λ pL promoter leads to a phenotypic switch.In λ red- gam-, transcription from the pL promoter proceeds rightward and the red and gam genes are not transcribed. Recombination between the two homeologous sequences leads to inversion of the pL-N segment causing a selectable phenotype (see Text for details). Not drawn to scale.
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pgen-1000065-g001: Recombination between the two homeologous oxa sequences flanking the λ pL promoter leads to a phenotypic switch.In λ red- gam-, transcription from the pL promoter proceeds rightward and the red and gam genes are not transcribed. Recombination between the two homeologous sequences leads to inversion of the pL-N segment causing a selectable phenotype (see Text for details). Not drawn to scale.

Mentions: To test the efficiency of homeologous recombination in virus genomes, we studied recombination between pairs of sequence diverged genes inserted into the genome of λ. The experimental system is based on a genetic switch in λ resulting from homologous recombination between two identical inversely oriented IS10 sequences flanking the promoter pL [23]. Recombination between such inverted repeats is accompanied by the inversion of the pL promoter, leading to a phenotypic switch used to score recombinants (Figure 1). In the normal pL orientation the red and gam genes are transcribed such that λ grows on a recA mutant host, but not on a P2 lysogen. In the opposite orientation of pL, red and gam are not expressed, and λ grows on a P2 lysogen, but not on a recA strain.


The lambda red proteins promote efficient recombination between diverged sequences: implications for bacteriophage genome mosaicism.

Martinsohn JT, Radman M, Petit MA - PLoS Genet. (2008)

Recombination between the two homeologous oxa sequences flanking the λ pL promoter leads to a phenotypic switch.In λ red- gam-, transcription from the pL promoter proceeds rightward and the red and gam genes are not transcribed. Recombination between the two homeologous sequences leads to inversion of the pL-N segment causing a selectable phenotype (see Text for details). Not drawn to scale.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2327257&req=5

pgen-1000065-g001: Recombination between the two homeologous oxa sequences flanking the λ pL promoter leads to a phenotypic switch.In λ red- gam-, transcription from the pL promoter proceeds rightward and the red and gam genes are not transcribed. Recombination between the two homeologous sequences leads to inversion of the pL-N segment causing a selectable phenotype (see Text for details). Not drawn to scale.
Mentions: To test the efficiency of homeologous recombination in virus genomes, we studied recombination between pairs of sequence diverged genes inserted into the genome of λ. The experimental system is based on a genetic switch in λ resulting from homologous recombination between two identical inversely oriented IS10 sequences flanking the promoter pL [23]. Recombination between such inverted repeats is accompanied by the inversion of the pL promoter, leading to a phenotypic switch used to score recombinants (Figure 1). In the normal pL orientation the red and gam genes are transcribed such that λ grows on a recA mutant host, but not on a P2 lysogen. In the opposite orientation of pL, red and gam are not expressed, and λ grows on a P2 lysogen, but not on a recA strain.

Bottom Line: However, the precise molecular processes underlying this mosaicism are unknown.To test this, we have measured the efficiency of homeologous recombination between diverged oxa gene pairs inserted into lambda.The recombination editing proteins, MutS and UvrD, showed only marginal effects on lambda recombination.

View Article: PubMed Central - PubMed

Affiliation: Faculté de Médecine R. Descartes, INSERM U571, Université Paris Descartes, Paris, France.

ABSTRACT
Genome mosaicism in temperate bacterial viruses (bacteriophages) is so great that it obscures their phylogeny at the genome level. However, the precise molecular processes underlying this mosaicism are unknown. Illegitimate recombination has been proposed, but homeologous recombination could also be at play. To test this, we have measured the efficiency of homeologous recombination between diverged oxa gene pairs inserted into lambda. High yields of recombinants between 22% diverged genes have been obtained when the virus Red Gam pathway was active, and 100 fold less when the host Escherichia coli RecABCD pathway was active. The recombination editing proteins, MutS and UvrD, showed only marginal effects on lambda recombination. Thus, escape from host editing contributes to the high proficiency of virus recombination. Moreover, our bioinformatics study suggests that homeologous recombination between similar lambdoid viruses has created part of their mosaicism. We therefore propose that the remarkable propensity of the lambda-encoded Red and Gam proteins to recombine diverged DNA is effectively contributing to mosaicism, and more generally, that a correlation may exist between virus genome mosaicism and the presence of Red/Gam-like systems.

Show MeSH
Related in: MedlinePlus