FORESPORE-SPECIFIC DISAPPEARANCE OF THE SIGMA-FACTOR ANTAGONIST SPOLLAB - IMPLICATIONS FOR ITS ROLE IN DETERMINATION OF CELL FATE IN BACILLUS-SUBTILIS

Endospore formation in Bacillus subtilis is a morphologically complex process in which the bacterium divides into two compartments (forespor e and mother cell) that follow different developmental paths. Compartm ent-specific transcription in the forespore is initiated by RNA polyme rase containing sigma(F), and results in the forespore-specific produc tion of sigma(G), which directs most of the subsequent forespore-speci fic transcription. The activity of sigma(F) is thought to be restricte d to the forespore by the sigma factor antagonist SpoIIAB. We used ant ibodies against SpoIIAB to monitor its accumulation during sporulation . We found that SpoIIAB accumulates early after the initiation of spor ulation, and that it was present in the mother-cell compartment 2 h af ter sigma(F) became active in the forespore. SpoIIAB disappeared prefe rentially from the forespore during development, and its disappearance from the forespore compartment correlated with the activation of (sig ma(G) in that compartment, raising the possibility that SpoIIAB may be involved regulating a G activity. We tested whether SpoIIAB could ant agonize sigma(G) activity by replacing the sigma(F)-dependent promoter that drives expression of spoIIIG, the structural gene for sigma(G), with a sigma(H)-dependent promoter. This resulted in a lytic phenotype that was supressed by the simultaneous expression of a plasmid-borne copy of spoIIAB. This suggests that SpoIIAB can suppress this effect o f sigma(G) expression. Moreover, these cells formed spores efficiently . Since sigma(G) synthesis in these cells was not restricted to the fo respore by the sigma(F)-dependent transcription of its structural gene that normally occurs in wild-type cells, the forespore-specific activ ity of sigma(G) required for sporulation appears to have resulted from expression of spoIIAB.