FIG. 2.

Regulation of transition-phase gene expression and a model for the possible regulation of the yqxM sipW tasA operon. (A) Summary of the roles of Spo0A, ς^H, and AbrB on transition-phase gene expression. The long arrow on the left indicates the influence of factors controlling the cellular concentration of Spo0A∼P, which in turn determines whether the cell will express sporulation (Spo) genes, competence (com) genes, or genes associated with another transition phase choice (on the right). Not all transition-phase genes are controlled directly by Spo0A. (B) A speculative model for transcriptional control of the operon. Spo0A and ς^H direct expression. Separately, an as yet unidentified additional sigma factor also directs expression. AbrB can repress both events. Although a single promoter is illustrated, multiple promoters may be present.