SpoVM, a small protein essential to development in Bacillus subtilis, interacts with the ATP-dependent protease FtsH

The spoVM gene encodes a 26-amino-acid polypeptide that is essential for spore formation in Bacillus subtilis. A transposon insertion within the spoVM open reading frame has been shown to encode a chimeric protein which is biologically inactive and produces a phenotype identical to that of a deletion and insertion mutation. A genetic approach was used to identify possible interacting proteins, and the membrane-bound FtsH protease was identified, Mutations in ftsH suppressed the sporulation defect of certain spoVM mutants but not others. However, production of the mother cell sigma factors, sigma(E) and sigma(K), was abnormal in the suppressed strains, and mutations in either spoVM or ftsH alone impaired sigma factor production and sporulation gene expression, Using FtsH purified from Escherichia coli, we demonstrated that in vitro (i) SpoVM inhibits FtsH protease activity and (ii) SpoVM is a substrate for the FtsH protease. We propose that during sporulation, SpoVM serves as a competitive inhibitor of FtsH activity, This interaction appears to be important for completion of the prespore engulfment step of sporulation, based on the phenotype of certain spoVM ftsH double mutants.