SigB, an RNA polymerase sigma factor required for osmoprotection and proper differentiation of Streptomyces coelicolor

Citation
Yh. Cho et al., SigB, an RNA polymerase sigma factor required for osmoprotection and proper differentiation of Streptomyces coelicolor, MOL MICROB, 42(1), 2001, pp. 205-214
Citations number
35
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Microbiology
Journal title
MOLECULAR MICROBIOLOGY
ISSN journal
0950-382X → ACNP
Volume
42
Issue
1
Year of publication
2001
Pages
205 - 214
Database
ISI
SICI code
0950-382X(200110)42:1<205:SARPSF>2.0.ZU;2-C
Abstract
A gene (sigB) encoding an alternative sigma factor sigma (B) in Streptomyce s coelicolor A3(2) was isolated and characterized. It encodes a polypeptide of 281 amino acids (31546 Da) and is highly homologous to Bacillus subtili s sigma (B). The sigB coding region is preceded by four open reading frames (ORFs): dpsA, orfA, rsbB and rsbA in sequential order. RNA analyses reveal ed that rsbB, rsbA and sigB constitute an operon (sigB operon). Transcripts were produced constitutively from a promoter (sigBp2) upstream of the rsbB coding region, contributing to the basal level expression of sigmaB protei n. An inducible promoter (sigBp1) resembling the catB promoter (catBp) was located between the rsbA and sigB coding regions. Transcripts from sigBp1 d ramatically increased as cells differentiated on solid media, at the statio nary phase in liquid media or by osmotic stresses similar to the behaviour of catBp transcripts. Both catBp and sigBp1 promoters were recognized speci fically by sigma (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 catBp is under the control of UB. The sigB mutant exhibited a similar phenotype to the ca tB mutant, being sensitive to hyperosmolarity, blocked in forming aerial my celium and with skewed antibiotic production. Therefore, we conclude that s igma (B) ensures the proper differentiation and osmoprotection of S. coelic olor cells, primarily via regulation of the expression of catalase B.