Carbon source-dependent regulation of the acetyl-coenzyme A synthetase-encoding gene ACSI from saccharomyces cerevisiae

Abstract

The yeast ACS1 gene, encoding acetyl-coenzyme A synthetase (ACS), was cloned using colony hybridization and a facA probe from Aspergillus nidulans. The complete sequence of 1.5 kb of the ACSI upstream region was determined. Northern hybridization revealed a strong derepression of ACSI transcripts in a strain grown on the nonfermentable carbon sources, acetate or ethanol. In contrast to a previous report, δacsl null mutants did not exhibit a growth defect on acetate medium. Indeed, enzyme assays showed the presence of an additional constitutively expressed ACS activity in Aacsl mutants. The carbon source-dependent expression was further investigated by the use of an ACSI::lacZ fusion gene, showing complete repression on easily fermentable sugars such as glucose, maltose, sucrose or galactose. Binding sites for the yeast general regulatory factors, Abflp and Reblp, together with a sequence reminiscent of the recently identified carbon source-responsive element ( CSRE), could be detected in the ACSI upstream region, presumably mediating the observed regulatory phenotype of this ACS isoenzyme.