TRANSCRIPTION FACTOR-SIGMA-B OF BACILLUS-SUBTILIS CONTROLS A LARGE STATIONARY-PHASE REGULON

Transcription factor sigma(B) of Bacillus subtilis is active during th e stationary growth phase, but its physiological role remains unknown. Understanding the function and regulation of genes controlled by sigm a(B) (csb genes) should provide important clues to sigma(B) function i n stationary-phase cells. To this end, we used a genetic approach to i dentify six new csb genes. This strategy relies on two elements: (i) r andom transcriptional fusions between the Escherichia coli lacZ gene a nd genes on the B. subtilis chromosome, generated in vivo with transpo son Tn917lacZ, and (ii) a plate transformation technique to introduce a null sigB mutation into the fusion-bearing recipients directly on in dicator plates. This strategy allowed the comparison of fusion express ion in strains that were isogenic save for the presence or absence of a functional sigma(B) protein. Beginning with 1,400 active fusions, we identified 11 that were wholly or partly controlled by sigma(B). Thes e fusions mapped to six different loci that exhibit substantial contra sts in their patterns of expression in the logarithmic and stationary growth phases, suggesting that they participate in diverse cellular fu nctions. However, for all six loci, the sigma(B)-dependent component o f their expression was manifest largely in the stationary phase. The h igh frequency of six independent csb loci detected in a random collect ion of 1,400 fusions screened, the fact that four of the six new loci were defined by a single fusion, and the absence of the previously ide ntified ctc and csbA genes in the present collection strongly suggest that sigma(B) controls a large stationary-phase regulon.