RecX Facilitates Homologous Recombination by Modulating RecA Activities

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 (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.枯草芽孢杆菌（Bacillus subtilis）recH342菌株可降低种间重组频率，且对同基因型DNA（homogamic DNA）的转化频率无显著影响。该菌株的推定recX（yfhG）基因携带一处点突变，此突变后续被命名为recX342。研究表明，由264个氨基酸残基构成的RecX蛋白（RecX）与变形杆菌门（Proteobacterial）来源的RecX蛋白存在部分序列同源性。RecX的缺失会严重削弱质粒DNA与染色体DNA介导的自然转化过程。实验证实，RecX可抑制重组酶A（RecA）在质粒转化过程中产生的负面效应，阻止RecA对单链DNA区域的错误识别，并调控DNA链交换反应。RecX通过调控RecA丝状体（RecA filament）的长度与组装紧密程度，促进重组过程的起始，并提升种间重组频率。