MOLECULAR-CLONING AND CHARACTERIZATION OF 2 GENES ENCODING SIGMA FACTORS THAT DIRECT TRANSCRIPTION FROM A BACILLUS-THURINGIENSIS CRYSTAL PROTEIN GENE PROMOTER

Two sigma factors, sigma-35 and sigma-28, direct transcription from the Bt I and Bt II promoters of the cryIA(a) gene of Bacillus thuringiensis; this gene encodes a lepidopteran-specific crystal protoxin. These sigma factors were biochemically characterized in previous work (K. L. Brown and H. R. Whiteley, Proc. Natl. Acad. Sci. USA 85:4166-4170, 1988; K. L. Brown and H. R. Whiteley, J. Bacteriol. 172:6682-6688, 1990). In this paper, we describe the cloning of the genes encoding these two sigma factors, as well as their nucleotide and deduced amino acid sequences. The deduced amino acid sequences of the sigma-35 and sigma-28 genes show 88 and 85% identity, respectively, to the sporulation-specific sigma-E and sigma-K polypeptides of Bacillus subtilis. Transformation of the sigma-35 and sigma-28 genes into B. subtilis shows that the respective B. thuringiensis sigma factor genes can complement spoIIG55 (sigma-E) and spoIIIC94 (sigma-K) defects. Further, B. thuringiensis core polymerase reconstituted with either the sigma-35 or sigma-28 polypeptide directs transcription from B. subtilis promoters recognized by B. subtilis RNA polymerase containing sigma-E and sigma-K, respectively. Thus, sigma-35 and sigma-28 of B. thuringiensis appear to be functionally equivalent to sigma-E and sigma-K of B. subtilis. However, unlike the situation for sigma-K in B. subtilis, the homologous sigma-28 gene in B. thuringiensis does not result from a late-sporulation-phase chromosomal rearrangement of two separate, partial genes.