Cloning and DNA sequence of sigB gene of Stigmatella aurantiaca

Stigmatella aurantiaca belongs to the myxobacteria, which, upon environmental stress, form species-specific fruiting bodies, containing myxospores. This communication reports the cloning and sequencing of the sigB gene, encoding a sigma-subunit of the DNA dependent RNA polymerase (RNAP). The gene was isolated from a lambda gt11 library of S. aurantiaca DNA by using an oligonucleotide as a hybridization probe, which corresponds to the highly conserved domain 2 of eubacterial sigma factors (amino acids IGLMKAV). This domain is thought to be involved in RNAP core binding and should be present also in minor sigma factors. The DNA sequence of the sigB gene was determined by the Sanger dideoxy method. The ORF encodes a polypeptide of 296 amino acids with a predicted molecular weight of 33,297. The alignment with other sigma-sequences shows that it belong to the heat shock sigma cluster.