Analysis of a Suppressor Mutationssb(kinC)ofsur0B20(spo0A) Mutation inBacillus subtilisReveals thatkinC Encodes a Histidine Protein Kinase

sur0B20 is a mutation that suppresses the effects of spo0BDB or spo0F221 mutations in Bacillus subtilis. sur0B20is an allele of thespo0Agene (Glu-14 to Val-14 conversion) and restores the sporulation ofspo0Bor spo0F mutants to the wild-type level. Here, we report the isolation of suppressor mutations ofsur0B20 (ssb). One of these mutations,ssb-12, severely impairs the suppressor activity ofsur0B20. A 2.5-kbpMboI fragment which complements thessb-12mutation was cloned by the prophage transformation method using fCM as a vector. Nucleotide sequencing of the fragment revealed two open reading frames (orf1 and orf2). Gene disruption and complementation experiments showed that orf2 is the ssb gene. ssb was shown to encode a protein with a molecular weight of 48,846 (428 amino acid residues) showing strong similarity to transmitter kinases, especially KinA, of two-component regulatory systems. Therefore,ssbwas renamedkinC. Deletion of kinC had no observable effect on sporulation. kinC transcription was induced at the onset of sporulation, probablyfroma s A -dependentpromoter,anditsexpressionwasshutoffatT3.DNaseIprotectionexperiments showedthattheSpo0AproteinbindstotwoadjoiningsitesinthekinCpromoterregionwithdifferentaffinities. These results suggest thatkinCexpression might be regulated by Spo0A.