A novel SMC-like protein,SbcE (YhaN), is involved in DNA double-strand break repair and competence in Bacillus subtilis

Bacillus subtilis and most Gram positive bacteria possess four SMC like proteins: SMC, SbcC, RecN and the product of the yhaN gene, termed SbcE. SbcE is most similar to SbcC but contains a unique central domain. We show that SbcE plays a role during transformation in competent cells and in DNA double-strand break (DSB) repair. The phenotypes were strongly exacerbated by the additional deletion of recN or of sbcC, suggesting that all three proteins act upstream of RecA and provide distinct avenues for presynapsis. SbcE accumulated at the cell poles in competent cells, and localized as a discrete focus on the nucleoids in 10% of growing cells. This number moderately increased after treatment with DNA damaging agents and in the absence of RecN or of SbcC. Damage-induced foci of SbcE arose early after induction of DNA damage and rarely colocalized with the replication machinery. Our work shows that SMC-like proteins in B. subtilis play roles at different subcellular sites during DNA repair. SbcC operates at breaks occurring at the replication machinery, whereas RecN and SbcE function mainly, but not exclusively, at DSBs arising elsewhere on the chromosome. In agreement with this idea, we found that RecN-YFP damage-induced assemblies also arise in the absence of ongoing replication.