ANALYSIS OF THE STREPTOMYCES-COELICOLOR SIGE GENE REVEALS THE EXISTENCE OF A SUBFAMILY OF EUBACTERIAL RNA-POLYMERASE SIGMA-FACTORS INVOLVEDIN THE REGULATION OF EXTRACYTOPLASMIC FUNCTIONS

sigma(E), an RNA polymerase a factor of apparent M(r) 28,000, was prev iously identified by its ability to direct transcription from the P2 p romoter of the agarase gene (dagA) of Streptomyces coelicolor. A degen erate oligonucleotide probe, designed from the N-terminal sequence of purified sigma(E), was used to isolate the sigma(E) gene (sigE). The p redicted sequence of sigma(E) shows greatest similarity to sequences o f seven other proteins: Myxococcus xanthus CarQ, Pseudomonas aeruginos a AlgU, Pseudomonas syringae HrpL, Escherichia coli sigma(E), Alcalige nes eutrophus CnrH, E. coli FecI, and Bacillus subtilis SigX, a protei n of unknown function. These eight proteins define a subfamily of euba cterial RNA polymerase factors sufficiently different from other sigma s that, in many cases, they are not identified by standard similarity searching methods. Available information suggests that all of them re gulate extracytoplasmic functions and that they function as effector m olecules responding to extracytoplasmic stimuli. A. eutrophus CnrH app ears to be a plasmid-encoded factor.