Expression of the ftsY gene, encoding a homologue of the alpha subunit of mammalian signal recognition particle receptor, is controlled by different promoters in vegetative and sporulating cells of Bacillus subtilis

Bacillus subtilis FtsY (Srb) is a homologue of the a subunit of the recepto r for mammalian signal-recognition particle (SRP) and is essential for prot ein secretion and vegetative cell growth. The ftsY gene is expressed during both the exponential phase and sporulation. In vegetative cells, ftsY is t ranscribed with two upstream genes, rncS and smc, that are under the contro l of the major transcription factor sigma (A). During sporulation, Northern hybridization detected ftsY mRNA in wild-type cells, but not in sporulatin g cells of sigma (K) and gerE mutants. Therefore, ftsY is solely expressed during sporulation from a sigma (K)- and GerE-controlled promoter that is l ocated immediately upstream of ftsY inside the smc gene. To examine the rol e of FtsY during sporulation, the B. subtilis strain ISR39 was constructed, a ftsY conditional mutant in which ftsY expression can be shut off during spore formation but not during the vegetative state. Electron microscopy sh owed that the outer coat of ISR39 spores was not completely assembled and i mmunoelectron microscopy localized FtsY to the inner and outer coats of wil d-type spores.