THE ROLE OF NEGATIVE CONTROL IN SPORULATION

Negative controls play an important role in the regulation of differentiation in many organisms. Sporulation in Bacillus subtilis is also regulated by DNA-binding proteins which exert a repressive effect on genes which are essential for this process. AbrB represses spoOH, coding for sigma(H). One of the earliest events in the initiation of sporulation is the lifting of this repression so that more sigma(H) can be made. As part of an RNA polymerase holoenzyme, this positive transcription factor is responsible for the elevated synthesis of sufficient phosphorylated SpoOA to activate the expression of several stage II genes. Sin, another DNA-binding protein, represses the same genes, spollA, spollE and spollG, that are activated by SpoOA. Thus sporulation is controlled at the two earliest stages by at least two repressors. Sin and AbrB are repressors of other late growth functions but are essential for competence development. Sin is also a positive regulator for motility and autolysin production. These results suggest that AbrB and Sin act as developmental switches, enabling cells at the beginning of stationary growth to choose different developmental fates.