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bThe GenBank accession number for the sequence reported in this paper is AB023642.
To identify negative regulatory genes for cellular differentiation in Streptomyces griseus, DNA fragments repressing the normal developmental processes were cloned on a high-copy-number plasmid. One of these DNA fragments markedly repressed aerial mycelium and spore formation on solid media containing glucose or galactose, but not on media containing maltose or mannitol. The fragment contained three complete ORFs; precise subcloning revealed that a 249 bp fragment located in the promoter region between ORF1 and ORF3 was sufficient for repression. Quantification of the promoter activities by using a thermostable malate dehydrogenase gene as a reporter showed that the promoter for ORF3 (PORF3) maintained high activity in mycelia grown in the presence of glucose but lost activity rapidly in maltose medium. PORF3 activity increased markedly when the promoter sequence was introduced on a high-copy-number plasmid. The results suggested that carbon-source-dependent deactivation of PORF3 mediated by a transcriptional repressor may initiate differentiation in S. griseus.
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