title: RecX facilitates homologous recombination by modulating RecA activities.
abstract: The Bacillus subtilis recH342 strain, which decreases interspecies recombination without significantly affecting the frequency of transformation with homogamic DNA, carried a point mutation in the putative recX (yfhG) gene, and the mutation was renamed as recX342. We show that RecX (264 residues long), which shares partial identity with the Proteobacterial RecX (<180 residues), is a genuine recombination protein, and its primary function is to modulate the SOS response and to facilitate RecA-mediated recombinational repair and genetic recombination. RecX-YFP formed discrete foci on the nucleoid, which were coincident in time with RecF, in response to DNA damage, and on the poles and/or the nucleoid upon stochastic induction of programmed natural competence. When DNA was damaged, the RecX foci co-localized with RecA threads that persisted for a longer time in the recX context. The absence of RecX severely impaired natural transformation both with plasmid and chromosomal DNA. We show that RecX suppresses the negative effect exerted by RecA during plasmid transformation, prevents RecA mis-sensing of single-stranded DNA tracts, and modulates DNA strand exchange. RecX, by modulating the "length or packing" of a RecA filament, facilitates the initiation of recombination and increases recombination across species.
authors.affiliation: Department of Microbial Biotechnology, Centro Nacional de Biotechnología, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
authors.forename: Paula P
authors.initials: PP
authors.lastname: Cárdenas
authors.forename: Begoña
authors.initials: B
authors.lastname: Carrasco
authors.forename: Clarisse
authors.initials: C
authors.lastname: Defeu Soufo
authors.forename: Carolina E
authors.initials: CE
authors.lastname: César
authors.forename: Katharina
authors.initials: K
authors.lastname: Herr
authors.forename: Miriam
authors.initials: M
authors.lastname: Kaufenstein
authors.forename: Peter L
authors.initials: PL
authors.lastname: Graumann
authors.forename: Juan C
authors.initials: JC
authors.lastname: Alonso
mesh_terms: D001412:Bacillus subtilis / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D004249:DNA Damage / Q000235:genetics; D059765:Homologous Recombination / Q000235:genetics*; D017354:Point Mutation; D011938:Rec A Recombinases / Q000235:genetics*; D013014:SOS Response, Genetics; D014169:Transformation, Bacterial
chemical_list: D001426:Bacterial Proteins; C430523:RecX protein, Xanthomonas campestris; D011938:Rec A Recombinases