A conserved ClpP ‐like protease involved in spore outgrowth in B acillus subtilis

Summary Germination and outgrowth of endospores of the G ram‐positive bacterium B acillus subtilis involves the degradation and conversion to free amino acids of abundant proteins located in the spore core known as small acid‐soluble proteins ( SASP ). This degradation is mediated primarily by the germination protease Gpr . Here we show that YmfB , a distant homologue of ClpP serine proteases that is highly conserved among endospore‐forming bacteria, contributes to SASP degradation but that its function is normally masked by Gpr . Spores from a ymfB gpr double mutant were more delayed in spore outgrowth and more impaired in SASP degradation than were spores from a gpr single mutant. The activity of YmfB relied on three putative active‐site residues as well as on the product of a small gene ylzJ located immediately downstream of, and overlapping with, ymfB . We propose that YmfB is an orphan ClpP protease that is dedicated to the degradation of a specialized family of small protein substrates.