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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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Related in: MedlinePlus

Frequency of recombinants in the RecABCD and the Red pathways, at different levels of sequence divergence, determined by single step growth of phages.Every bar shows the mean and standard deviation deduced from at least three experiments.
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pgen-1000065-g002: Frequency of recombinants in the RecABCD and the Red pathways, at different levels of sequence divergence, determined by single step growth of phages.Every bar shows the mean and standard deviation deduced from at least three experiments.

Mentions: In the RecABCD pathway, maximum inversion frequency was 3×10−4 for identical sequences, whereas the minimum measured was 3×10−6 for 22% divergence (Figure 2). Unexpectedly, the recombinant frequency was as high between 4% diverged sequences as between identical sequences, and this effect persisted in the mutS background (see Table 1). A 4% divergence was reported to reduce by 1000 fold homologous recombination in the E. coli chromosome [29]. No obvious sequence stimulating recombination, such as a Chi site, is present in the oxa11 sequence used to construct the 4% diverged substrate. Rather than being a stimulation of recombination between 4% diverged sequences, it could be that some process inhibits recombination between the strictly identical sequences in λ.


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

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

Frequency of recombinants in the RecABCD and the Red pathways, at different levels of sequence divergence, determined by single step growth of phages.Every bar shows the mean and standard deviation deduced from at least three experiments.
© Copyright Policy
Related In: Results  -  Collection

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

pgen-1000065-g002: Frequency of recombinants in the RecABCD and the Red pathways, at different levels of sequence divergence, determined by single step growth of phages.Every bar shows the mean and standard deviation deduced from at least three experiments.
Mentions: In the RecABCD pathway, maximum inversion frequency was 3×10−4 for identical sequences, whereas the minimum measured was 3×10−6 for 22% divergence (Figure 2). Unexpectedly, the recombinant frequency was as high between 4% diverged sequences as between identical sequences, and this effect persisted in the mutS background (see Table 1). A 4% divergence was reported to reduce by 1000 fold homologous recombination in the E. coli chromosome [29]. No obvious sequence stimulating recombination, such as a Chi site, is present in the oxa11 sequence used to construct the 4% diverged substrate. Rather than being a stimulation of recombination between 4% diverged sequences, it could be that some process inhibits recombination between the strictly identical sequences in λ.

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