title: Distinctive features of homologous recombination in an 'old' microorganism, Lactococcus lactis.
abstract: Homologous recombination is needed to assure faithful inheritance of DNA material, especially under stress conditions. The same enzymes that repair broken chromosomes via recombination also generate biodiversity. Their activities may result in intrachromosomal rearrangements, assimilation of foreign DNA, or a combination of these events. It is generally supposed that homologous recombination systems are conserved, and function the same way everywhere as they do in Escherichia coli, the accepted paradigm. Studies in an 'older' microorganism, the gram-positive bacterium of the low GC branch Lactococcus lactis, confirm that many enzymes are conserved across species lines. However, the main components of the double strand break (DSB) repair system, an exonuclease/helicase (Exo/hel) and a short DNA modulator sequence Chi, differ markedly between bacteria, especially when compared to the gram-negative analogues. Based on our studies, a model is proposed for the functioning of the two-subunit Exo/hel of L. lactis and other gram-positive bacteria, which differs from that of the three-subunit E. coli enzyme. The differences between bacterial DSB repair systems may underlie a selection for diversity when dealing with DSB. These and other features of homologous recombination in L. lactis are discussed.
authors.affiliation: Laboratoire de génétique appliquée, Institut national de la recherche agronomique, Jouy en Josas, France.
authors.forename: A
authors.initials: A
authors.lastname: Quiberoni
authors.forename: L
authors.initials: L
authors.lastname: Rezaïki
authors.forename: M
authors.initials: M
authors.lastname: El Karoui
authors.forename: I
authors.initials: I
authors.lastname: Biswas
authors.forename: P
authors.initials: P
authors.lastname: Tailliez
authors.forename: A
authors.initials: A
authors.lastname: Gruss
mesh_terms: D001435:Bacteriophages / Q000502:physiology; D004265:DNA Helicases / Q000378:metabolism; D004260:DNA Repair; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D017753:Ecosystem; D004706:Endodeoxyribonucleases / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000378:metabolism; D014644:Genetic Variation; D013294:Lactococcus lactis / Q000235:genetics* / Q000378:metabolism / Q000821:virology; D011995:Recombination, Genetic
chemical_list: D004269:DNA, Bacterial; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V; D004265:DNA Helicases