Proteolysis of the replication checkpoint protein Sda is necessary for the efficient initiation of sporulation after transient replication stress in Bacillus subtilis

Cells of Bacillus subtilis actively co-ordinate the initiation of sporulation with DNA replication and repair. Conditions that perturb replication initiation or replication elongation induce expression of a small protein, Sda, that specifically inhibits the histidine kinases required to initiate spore development. Previously, the role of Sda has been studied during chronic blocks to DNA replication. Here we show that induction of Sda is required to delay the initiation of sporulation when replication elongation is transiently blocked or after UV irradiation. During the recovery phase, cells efficiently sporulated, but this required the proteolysis of Sda. The rapid proteolysis of Sda required the ClpXP protease and the uncharged C-terminal sequence of Sda. Replacing the last two residues of Sda, both serines, with aspartic acids markedly stabilized Sda. Strains expressing sdaDD from the endogenous sda locus were unable to efficiently initiate sporulation after transient replication stress. We conclude that the Sda replication checkpoint is required to delay the initiation of sporulation when DNA replication is transiently perturbed, and that the intrinsic instability of Sda contributes to shutting off the pathway. The Sda checkpoint thus co-ordinates early events of spore development, including the polar cell division, with successful completion of chromosome replication.