ADHII in Aspergillus nidulans is induced by carbon starvation stress

In Aspergillus nidulans there are three NAD(+)-dependent alcohol dehydrogenases (ADHs) that are capable of utilizing ethanol as a substrate. ADHI is the physiological enzyme of ethanol catabolism and ADHIII is induced under conditions of anaerobiosis. The physiological role of ADHII (structural gene alcB) is unknown. We have measured beta-galactosidase in a transformant with an alcB::lacZ fusion and have shown that alcB is maximally expressed under conditions of carbon starvation. The behavior of the alcB::lacZ transformant suggests a hierarchy of repressing carbon sources characteristic of repression by the general carbon catabolite repressor protein, CreA, but in a creA(d)30 background the transformant shows only partial derepression of beta-galactosidase on 1% glucose compared to the creA+ strain. Our results suggest that, in addition to carbon catabolite repression acting via CreA, a CreA-independent mechanism is involved in induction of alcB on carbon starvation.