Cloning and characterization of the gene encoding the major sigma factor of Stigmatella aurantiaca

Abstract

The gene ( sigA) encoding the major σ factor of the myxobacterium, Stigmatella aurantiaca, was cloned and sequenced. The deduced polypeptide contains 706 amino acids (aa) and has a deduced M r of 79910. It exhibits four different aa sequence motifs which correlate with the conserved domains of the major σ factors of Myxococcus xanthus (σ 80), Escherichia coli (σ 70) and Bacillus subtilis (σ 43). The a factor (σ a) was detected in crude lysates of vegetative cells and in cells of different developmental stages from S. aurantiaca with an antiserum to M. xanthus σ 80 by Western blot analysis. The SigA polypeptide copurified with RNA polymerase from vegetative S. aurantiaca cells. The aa sequence of its N terminus matches a sequence located 25 codons downstream from the proposed start codon. The sigA gene was expressed in E. coli and the corresponding gene product cross-reacted with the SigA antiserum as a polypeptide of 100 kDa, which is identical in size to the σ A detected in vegetative cells of S. aurantiaca.