Abstract
We cloned a new gene, sigH, encoding an alternative σ factor in Streptomyces coelicolor A3(2). The deduced protein of 354 amino acids with an M r of 39 486 showed greatest similarity to the sporulation σ factor (σ F) of S. coelicolor, general stress-response σ B of Bacillus subtilis, and stationary-phase stress-response σ F of Mycobacterium tuberculosis. Sequence analysis of the upstream region revealed an ORF encoding a protein (UshX) similar to several anti-σ factors, and short ORF (UshY) containing zinc-finger DNA binding motif. Transcriptional analysis revealed that all three genes are located on the same polycistronic transcript in order ushY, ushX, and sigH. Expression of the operon was directed by four promoters differentially expressed in the course of differentiation. The first (P1) constitutive promoter was located upstream of ushY. The other three promoters (P2, P3, and P4) were located upstream of ushX, and were differentially induced after various stress conditions. The magnitude of the induction was greatest after osmotic stress and heat shock.
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