Carbon source regulation of a dextranase gene from the filamentous fungus Penicillium minioluteum.
The regulation of dextranase (dexA) gene expression in the filamentous fungus Penicillium minioluteum grown on different carbon sources was studied. Growth in the presence of dextran leads to high expression of the dextranase enzyme, but growth in starch, glucose, glycerol, lactose and sorbitol did not. Dextran induced dexA gene expression at the mRNA level. However, in cultures containing dextran plus glucose or glycerol, the transcript was detected 24 h later than in the case where dextran was the only carbon source. When the glucose or glycerol concentration in the dextran-containing medium was kept at about 1% (w/v), no dextranase-transcripts were detected. It was found that both glucose and glycerol inhibited enzyme synthesis, because 1% (w/v) addition of both carbon sources to dextran-growing cultures was able to abolish the inducing effect of dextran. Our results suggest that dextran utilization responds to both specific induction and to glucose and glycerol repression, providing evidence that P. minioluteum dexA expression is regulated by the carbon source at the transcriptional level.