Carbon regulation of penicillin biosynthesis in Aspergillus nidulans: a minor effect of mutations in creB and creC.

Transcription of the Aspergillus nidulans ipnA gene is under carbon regulation. Loss-of-function mutations in creB or creC do not cause full derepression of ipnA transcript levels in sucrose-grown mycelia and do not elevate repressed penicillin levels, indicating that neither of these genes plays a major regulatory role in penicillin biosynthesis. However, these mutations reduce external pH acidification, accelerate sucrose degradation and result in extracellular accumulation of resulting D-glucose and D-fructose. These effects would explain the partial elevation of carbon-repressed ipnA transcript levels observed in strains carrying creB- or creC- mutations.