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SigB, an RNA polymerase sigma factor required for osmoprotection and proper differentiation of Streptomyces coelicolor
Author(s) -
Cho YouHee,
Lee EunJin,
Ahn BoEun,
Roe JungHye
Publication year - 2001
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2001.02622.x
Subject(s) - streptomyces coelicolor , biology , sigma factor , operon , mutant , rna polymerase , gene , rna , microbiology and biotechnology , gene expression , open reading frame , promoter , genetics , peptide sequence
A gene ( sigB ) encoding an alternative sigma factor σ B in Streptomyces coelicolor A3(2) was isolated and characterized. It encodes a polypeptide of 281 amino acids (31 546 Da) and is highly homologous to Bacillus subtilis σ B . The sigB coding region is preceded by four open reading frames (ORFs): dpsA , orfA , rsbB and rsbA in sequential order. RNA analyses revealed that rsbB , rsbA and sigB constitute an operon ( sigB operon). Transcripts were produced constitutively from a promoter ( sigB p2) upstream of the rsbB coding region, contributing to the basal level expression of σ B protein. An inducible promoter ( sigB p1) resembling the catB promoter ( catB p) was located between the rsbA and sigB coding regions. Transcripts from sigB p1 dramatically increased as cells differentiated on solid media, at the stationary phase in liquid media or by osmotic stresses similar to the behaviour of catB p transcripts. Both catB p and sigB p1 promoters were recognized specifically by σ B ‐containing RNA polymerase in vitro . Disruption of the sigB gene abolished not only the differentiation‐associated expression but also the osmotic induction of the catB gene, indicating that catB p is under the control of σ B . The sigB mutant exhibited a similar phenotype to the catB mutant, being sensitive to hyperosmolarity, blocked in forming aerial mycelium and with skewed antibiotic production. Therefore, we conclude that σ B ensures the proper differentiation and osmoprotection of S. coelicolor cells, primarily via regulation of the expression of catalase B.