Summary: Glucose repressed transcription of the penicillin biosynthesis genes and when added at inoculation time to cultures of AS-P-78 but it had little repressive effect when added at 12 h and no effect when added at 24 or 36 h. A slight increase in the expression of and (and to a smaller extent of ) was observed in glucose-grown cultures at pH 6·8, 7·4 and 8·0 as compared with pH 6·2, but alkaline pHs did not override the strong repression exerted by glucose. Transcription of the actin gene used as control was not significantly affected by glucose or alkaline pHs. Repression by glucose of the three penicillin biosynthetic genes was also observed using the reporter gene coupled to each of the three promoters in monocopy transformants with the constructions integrated at the locus. Glucose repression of the three genes encoding enzymes of penicillin biosynthesis therefore appears to be exerted by a regulatory mechanism independent from pH regulation.


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