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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

Involvement of sigma(H) and related sigma factors in glucose-dependent initiation of morphological and physiological development of Streptomyces griseus.

We cloned and characterized sigH encoding a stress-response sigma factor, sigma(H), of Streptomyces griseus. Nucleotide sequencing of the sigH gene cluster revealed an identical gene organization as in the orthologous region of Streptomyces coelicolor A3(2). Transcriptional analysis by S1 nuclease mapping showed the presence of three tandem promoters (P1-P3) that direct transcription of sigH. The activity of P1 was markedly reduced in a sigH-depleted mutant, suggesting its dependence on sigma(H). P1 was induced by addition of 0.7 M NaCl, and P2 was induced by heat shock at 45 degrees C or addition of 4% ethanol. The sigH mutant of S. griseus showed conditional defect in aerial mycelium formation and streptomycin production depending on high concentration of glucose (>2%). Meanwhile, the wild-type strain of S. griseus introduced with rshA encoding a probable anti-sigma factor for sigma(H) on a high-copy-number plasmid was unable to perform development on media containing 1% glucose while it showed wild-type phenotype on media containing 1% maltose. RshA inhibited the sigma(H)-dependent in vitro run-off transcription at P1, which confirmed its role as a negative regulator for sigma(H). Analysis of RshA-sigma interaction by an Escherichia coli two-hybrid system showed specific interaction of RshA with sigma(H) and two related sigma factors, sigma(L) and sigma(F). We speculate that the high copy number of rshA represses morphological and physiological development of S. griseus through simultaneous inactivation of sigma(H) and related stress-response sigma factors, which play an essential role in the onset of cellular differentiation and antibiotic production on glucose media.[1]


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