Suppression of temperature-sensitive sporulation mutation in the Bacillus subtilis sigA gene by rpoB mutation

Abstract

We isolated a temperature-sensitive sporulation defective mutant of the sigA gene, encoding a major sigma factor, σ A protein, in Bacillus subtilis, and designated it as sigA21. The sigA21 mutation caused a single-amino acid substitution, E314K, in region 4 of the σ A protein. In this mutant, expression of the spoIIG gene, whose transcription depends on both σ A and the phosphorylated Spo0A protein, Spo0A∼P, a major transcription factor during early stages of sporulation, was greatly reduced at 43°C. To obtain further information on the mechanism of σ A function during the early spore development, we isolated a spontaneous sporulation-proficient suppressor mutant at 43°C. This extragenic suppressor mutation was mapped within the rpoB gene, encoding the β subunit of RNA polymerase, and was found to have a single-amino acid substitution, A863G. In this mutant, the expression of the spoIIG is partially restored at 43°C.