Mutational analysis of the precursor-specific region of Bacillus subtilis sigma E

sigma E is a sporulation-specific sigma factor of Bacillus subtilis that is formed from an inactive precursor protein (pro-sigma E) by the removal of 27 to 29 amino acids from the pro-sigma E amino terminus. By using oligonucleotide-directed mutagenesis, sequential deletions were constructed in the precursor-specific region of sigE and analyzed for their effect on the gene product's activity, ability to accumulate, and susceptibility to conversion into mature sigma E. The results demonstrated that the first 17 residues of the pro sequence contribute to silencing the sigma-like activity of pro-sigma E and that the amino acids between positions 12 and 17 are also important for its conversion into sigma E. Deletions that remove 21 or more codons from sigE reduce sigma E activity in cells which carry it, presumably by affecting pro-sigma E stability. A 26-codon deletion results in a gene whose product is not detectable in B. subtilis by either reporter gene activity or Western blot (immunoblot) assay. The primary structure as well as the size of the pro region of sigma E contributes to the protein's stability. The placement of additional amino acids into the pro region reduces the cell's ability to accumulate pro-sigma E. Additional sigE mutations revealed that the amino acids normally found at the putative processing site(s) of pro-sigma E are not essential to the processing reaction; however, a Glu residue upstream of these sites (position 25) was found to be important for processing. These last results suggest that the pro-sigma E processing apparatus does not recognize the actual site within pro-sigma E at which cleavage occurs but rater sequence elements that are upstream of this site.