Biology subjects

Rousseau, P.

Publications and source records attributed to Rousseau, P..

4 recordsLinked to original sources

bioRxiv2024

A mechanistic step in the genesis of secondary chromosomes from plasmids

Bacterial genomes contain a plethora of secondary replicons of divergent size. Circular replicons must carry a system for resolving dimeric forms, resulting from recombination between sister copies. These systems use site-specific recombinases. Among these, the XerCD recombinase resolves dimers of chromosomes and certain plasmids using different controls. We have analyzed the dimer resolution functions in enterobacterial secondary replicons and show that, in addition to the main chromosomes, XerCD is preferentially used by small plasmids and by the largest secondary replicons, megaplasmids and secondary chromosomes. Indeed, all replicons longer than 250 kb host an active XerCD recombination site. These sites, in contrast to those of small plasmids, use the same control as chromosomes, coupled to cell division by the FtsK protein. We conclude that a chromosome-like mode of dimer resolution is mandatory for the faithful inheritance of large plasmids and chromids, its acquisition being a prerequisite for the genesis of secondary chromosomes from plasmids.

microbiology↗

bioRxiv2023

Characterisation and reprogramming of bacteriophage mv4 integrase recombination specificity

Bacteriophage mv4 is a temperate bacterial virus able to integrate its genome at the 3 end of the tRNASER of Lactobacillus delbrueckii subsp. bulgaricus chromosome through site-specific recombination. Previous investigations revealed that the mv4Int/attP/attB recombination module was atypical compared to conventional heterobivalent tyrosine recombinases, such as the paradigmatic Lambdavirus lambda integrase, suggesting alternative recombination mechanism. In vitro recombination assays with random DNA libraries were used to comprehensively delineate the mv4 recombination system. We showed that mv4Int is a 369-aa protein that exhibits all structural hallmarks of integrases from the Tn916 family and interacts cooperatively with its recombination sites. We established that mv4Int distinguishes itself from classical heterobivalent integrases by a greater tolerance to nucleotide variations in attB and core-attP sites. We demonstrated that, upon considering nucleotide degeneracy, the 21-bp core-attP and attB recombination sites share structural similarities with classical heterobivalent integrase systems, with two 7-bp inverted-repeat regions corresponding to mv4Int core-binding sites surrounding a 7-bp strand-exchange region. Furthermore, our study highlighted compositional biases and nucleotide interdependencies within the core-binding regions that exerted a significant influence on the outcomes of recombination events.

molecular biology↗

bioRxiv2019

An improved Xer-cise technology for the generation of multiple unmarked mutants in Mycobacteria

Xer-cise is a technique using antibiotic resistance cassettes flanked by dif sites allowing spontaneous and accurate excision from bacterial chromosomes with a high frequency through the action of the cellular recombinase XerCD. Here, we report a significant improvement of Xer-cise in Mycobacteria. Zeocin-resistance cassettes flanked by variants of the natural Mycobacterium tuberculosis dif site were constructed and shown to be effective tools to construct multiple unmarked mutations in M. tuberculosis and in the model species Mycobacterium smegmatis. The dif site variants harbor mutations in the central region and can therefore not recombine with the wild type or other variants, resulting in mutants of increased genetic stability. The herein described method should be generalizable to virtually any transformable bacterial species.\n\nMethod summarydif-ZeoR-dif cassettes are used to replace non-essential genes in mycobacterial genome through recombineering. Spontaneous excision of the cassette is carried out under the action of the recombinase XerCD, resulting in unmarked deletions. Subsequent rounds of mutagenesis using cassettes flanked by a range of dif site variants allow construction of multiple mutants in which the different dif sites cannot recombine which each other, yielding stable genetic constructs.

microbiology↗

bioRxiv2019

Multiple activities of the MatP protein are involved in post-replicative pairing of sister chromosomes in Escherichia coli

The ter region of the bacterial chromosome, where replication terminates, is the last to be segregated before cell division in Escherichia coli. Delayed segregation is controlled by the MatP protein, which binds to specific sites (matS) within ter, and interacts with other proteins such as ZapB. Here, we investigate the role of MatP by combining short-time mobility analyses of the ter locus with biochemical approaches. We find that ter mobility is similar to that of a non-ter locus, except when sister ter loci are paired after replication. This effect depends on MatP, the persistence of catenanes, and ZapB. We characterise MatP/DNA complexes and conclude that MatP binds DNA as a tetramer, but bridging matS sites in a DNA-rich environment remains infrequent. We propose that tetramerisation of MatP links matS sites with ZapB and/or with non-specific DNA to promote optimal pairing of sister ter regions until cell division.Competing Interest StatementThe authors have declared no competing interest.View Full Text

microbiology↗