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 alpha subunit of the receptor for mammalian signal-recognition particle (SRP) and is essential for protein secretion and vegetative cell growth. The ftsY gene is expressed during both the exponential phase and sporulation. In vegetative cells, ftsY is transcribed with two upstream genes, rncS and smc, that are under the control of the major transcription factor sigma(A). During sporulation, Northern hybridization detected ftsY mRNA in wild-type cells, but not in sporulating cells of sigma(K) and gerE mutants. Therefore, ftsY is solely expressed during sporulation from a sigma(K)- and GerE-controlled promoter that is located immediately upstream of ftsY inside the smc gene. To examine the role 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 showed that the outer coat of ISR39 spores was not completely assembled and immunoelectron microscopy localized FtsY to the inner and outer coats of wild-type spores.