SPOIVB HAS 2 DISTINCT FUNCTIONS DURING SPORE FORMATION IN BACILLUS-SUBTILIS

The Bacillus subtilis SpoIVB protein is a critical component of the in tercompartmental signal-transduction pathway that activates the sigma factor, sigma(K), in the mother cell of the sporulating cell. SpoIVB, synthesized in the forespore chamber, must act across two layers of ph ospholipid membrane to facilitate proteolytic processing of inactive p ro-sigma(K) to active sigma(K). We have used a genetic approach to dis sect SpoIVB function and found that this protein has two distinct deve lopmental functions. One function is that of intercompartmental signal ling of pro-sigma(K) processing. The other role is essential to spore formation and is illustrated by mutations of SpoIVB which allow cell-c ell signalling of pro-sigma(K) processing but prevent the formation of viable spores. Using localized and site-specific mutagenesis we have identified a functional domain of SpoIVB that is involved in its non-s ignalling role.