GROWTH PHASE-REGULATED EXPRESSION OF BOLA AND MORPHOLOGY OF STATIONARY-PHASE ESCHERICHIA-COLI-CELLS ARE CONTROLLED BY THE NOVEL SIGMA FACTOR SIGMA-S

The novel sigma factor (sigma-S) encoded by rpoS (katF) is required for induction of many growth phase-regulated genes and expression of a variety of stationary-phase phenotypes in Escherichia coli. Here we demonstrate that wild-type cells exhibit spherical morphology in stationary phase, whereas rpoS mutant cells remain rod shaped and are generally larger. Size reduction of E. coli cells along the growth curve is a continuous and at least biphasic process, the second phase of which is absent in rpoS-deficient cells and correlates with induction of the morphogene bolA in wild-type cells. Stationary-phase induction of bolA is dependent on sigma-S. The "gearbox," a characteristic sequence motif present in the sigma-S-dependent growth phase- and growth rate-regulated bolAp1 promoter, is not recognized by sigma-S, since stationary-phase induction of the mcbA promoter, which also contains a gearbox, does not require sigma-S, and other sigma-S-controlled promoters do not contain gearboxes. However, good homology to the potential -35 and -10 consensus sequences for sigma-S regulation is found in the bolAp1 promoter.