Bacillus subtilis serine/threonine protein kinase YabT is involved in spore development via phosphorylation of a bacterial recombinase

We characterized YabT, a serine/threonine kinase of the Hanks family, from Bacillus subtilis. YabT is a putative transmembrane kinase that lacks the canonical extracellular signal receptor domain. We demonstrate that YabT possesses a DNA-binding motif essential for its activation. In vivo YabT is expressed during sporulation and localizes to the asymmetric septum. Cells devoid of YabT sporulate more slowly and exhibit reduced resistance to DNA damage during sporulation. We established that YabT phosphorylates DNA-recombinase RecA at the residue serine 2. A non-phosphorylatable mutant of RecA exhibits the same phenotype as the ΔyabT mutant, and a phosphomimetic mutant of RecA complements ΔyabT, suggesting that YabT acts via RecA phosphorylation in vivo. During spore development, phosphorylation facilitates the formation of transient and mobile RecA foci that exhibit a scanning-like movement associated to the nucleoid in the mother cell. In some cells these foci persist at the end of spore development. We show that persistent RecA foci, which presumably coincide with irreparable lesions, are mutually exclusive with the completion of spore morphogenesis. Our results highlight similarities between the bacterial serine/threonine kinase YabT and eukaryal kinases C-Abl and Mec1, which are also activated by DNA, and phosphorylate proteins involved in DNA damage repair.