No abstract

The product of the abrB gene of Bacillus subtilis is an ambiactive repressor and activator of the transcription of genes expressed during the transition state between vegetative growth and the onset of stationary phase and sporulation. Purified AbrB protein binds specifically in a highly co‐operative fashion to fragments of DNA containing the promoters it affects. DNase I footprints of the binding regions in these promoters revealed large protected areas of 50‐120 nucleotides or more depending on the promoter. Methylation protection experiments gave protected guanine residues on only one face of the DNA helix. A consensus sequence could be deduced around these guanine residues that was not found around non‐protected guanine residues in the footprint region. The results suggested that stationary phase functions and sporulation are repressed during active growth by AbrB and other transition state regulators by binding to the affected promoters in a concentration‐dependent manner.

The kinA (spoIIJ) locus contains a single gene which codes for a protein of 69,170 daltons showing strong homology to the transmitter kinases of two component regulatory systems. The purified kinase autophosphorylates in the presence of ATP and mediates the transfer of phosphate to the SpoOA and SPOOF sporulation regulatory proteins. SpoOF protein was a much better phosphoreceptor for this kinase than SpoOA protein in vitro. Mutants with deletion mutations in the kinA gene were delayed in their sporulation. They produced about a third as many spores as the wild type in 24 h, but after 72 h on solid medium, the level of spores approximated that found for the wild-type strain. Such mutations had no effect on the regulation of the abrB gene or on the timing of subtilisin expression and therefore did not impair the repression function of the SpoOA protein.Placement of the kinA locus on a multicopy vector suppressed the sporulation-defective phenotype of spoOB, spoOE, and spoOF mutations but not of spoOA mutations. The results suggest that the spoOB-, spoOE-, and spoOF-dependent pathway of activation (phosphorylation) of the SpoOA regulator may be by-passed through the kinA gene product if it is present at sufficiently high intracellular concentration. The results suggest that multiple kinases exist for the SpoOA protein.