Characterization of the gene encoding an intracellular proteinase inhibitor of Bacillus subtilis and its role in regulation of the major intracellular proteinase.

The gene (ipi) for an intracellular proteinase inhibitor (BsuPI) from Bacillus subtilis was cloned and found to encode a polypeptide consisting of 119 amino acids with no cysteine residues. The deduced amino acid sequence contained the N-terminal amino acid sequence of the inhibitor, which was chemically determined previously, and showed no significant homology to any other proteinase inhibitors. Analysis of the transcription initiation site and mRNA showed that the ipi gene formed an operon with an upstream open reading frame with an unknown function. The transcriptional control of ipi gene expression was demonstrated by Northern (RNA) blot analysis, and the time course of transcriptional enhancement roughly corresponded to the results observed at the protein level. Strains in which the ipi gene was disrupted or in which BsuPI was overexpressed constitutively sporulated normally. Analysis of the time course of production of the intracellular proteinase and proteinase inhibitor in these strains suggested that BsuPI directly regulated the major intracellular proteinase (ISP-1) activity in vivo.