TRANSCRIPTIONAL REGULATION OF THE 4 PROMOTERS OF THE AGARASE GENE (DAGA) OF STREPTOMYCES-COELICOLOR-A3(2)

The agarase gene (dagA) of Streptomyces coelicolor A3(2) is transcribe d from four promoters that are recognized by at least three. and proba bly four, different RNA polymerase holoenyzmes, each containing a diff erent sigma factor. S-1 nuclease protection studies revealed that tran scription from all four promoters is induced by the products of agar h ydrolysis and strongly repressed by glucose. Mutants deficient in gluc ose kinase activity were defective in glucose repression of all four p romoters. Mutants were isolated or identified in which transcription f rom all four promoters had become inducer-independent (i.e. constituti ve), establishing the existence of a repressor gene for dagA that does not appear to be located within 9 kb of the structural gene. The clon ed dagA gene was also constitutively expressed in the closely related strain Streptomyces lividans, which does not normally make agarase and which presumably lacks the repressor gene. Glucose was still able to repress dagA transcription even under conditions of constitutive expre ssion, suggesting that glucose kinase does not mediate its effect via inducer exclusion. Relative differences in the use of the four promote rs were not detected during different stages of growth of surface-grow n cultures, although dagA transcription appeared to peak during the pr oduction of aerial mycelium.