1998 Volume 124 Issue 1 Pages 98-104
Through mainly in vivo studies, the initiation of sporulation in Bacillus subtilis has been shown to depend on the phosphorylation of the SpoOA transcription factor mediated by the multicomponent phosphorelay via KinAB (C), SpoOF, SpoOB, and SpoOA in this order. RNA polymerase containing σA (EσA) or σH (EσH) transcribes the genes of the phosphorelay components. Phosphorylated SpoOA is also involved in their expression and is required for the induction of σH by repressing its repressor gene abrB. We have examined the effects of phosphorylated SpoOA (SpoOA-P) and AbrB on in vitro transcription of the genes involved in the SpoOA phosphorylation and initiation of sporulation. SpoOA-P repressed EσA-dependent transcription of the kinC and EσH-dependent transcription of spoOA and kinA. EσH-dependent transcription of spoOF was stimulated by SpoOA-P at low concentrations but was repressed by higher amounts of SpoOA-P. On the other hand, AbrB repressed EσA-dependent transcription of spoOH (σH gene), kinC, and abrB, although its effect was not strong. With the present results providing in vitro evidence for the roles of SpoOA-P and AbrB as transcriptional regulators, and other results described in the literature, the positive and negative feedback loops controlling the temporal expression of early sporulation genes are discussed.