Four genes in Streptomyces aureofaciens containing a domain characteristic of principal sigma factors.

Four genes encoding sigma-factor-like proteins, hrdA, hrdB, hrdD, and hrdE, were identified in a Streptomyces aureofaciens genomic library using an oligodeoxyribonucleotide probe encoding a peptide motif homologous to the core-binding domain in sigma factors. The deduced proteins have M(r) values of 43,363, 57,172, 36,591, and 57,565, respectively, and strongly resemble all known principal sigma factors, including possession of the characteristic 'rpoD box'. Transcription analysis of the hrd genes by Northern blot hybridization indicated only the expression of hrdB and hrdD and weak transcription of hrdA. A repetitive region of a pentapeptide tandemly repeated 6 and 4 times was identified in the N-terminal part of HrdB and HrdE, respectively. No such domain was found in any principal sigma factors.