Effects of amino acid substitutions in the promoter -10 binding region of the sigma A factor on growth of Bacillus subtilis.

On the bases of structural and functional information about the Bacillus subtilis sigma A protein and the techniques of site-directed mutagenesis, we constructed a B. subtilis sigA mutant (DB1005) which grows normally at 37 degrees C but is sensitive to higher temperatures. DNA sequencing analyses revealed that DB1005 has Ile-198-->Ala and Ile-202-->Ala amino acid substitutions in the alpha-helix of the 2.4 region of the sigma A protein. Western blotting (immunoblotting) revealed that this mutant sigma A protein is stable at both 37 and 49 degrees C. These results suggest that Ile-198 and Ile-202 separately or in combination are critical for the sigma A protein to be functional at the restrictive temperature.