EXPRESSION OF THE FOX1 GENE OF SACCHAROMYCES-CEREVISIAE IS REGULATED BY CARBON SOURCE, BUT NOT BY THE KNOWN GLUCOSE REPRESSION GENES

We have investigated the regulation of expression of the FOX1 gene of Saccharomyces cerevisiae which encodes acyl-CoA oxidase, the first enz yme in the peroxisomal beta oxidation of fatty acids. We have found th at the FOX1 steady state mRNA level is repressed by glucose, partially induced by ethanol (but not by raffinose) and fully induced by oleic acid as a carbon source. Glucose repression was observed even if cultu res were grown to stationary phase; however, if the glucose supply was limited initially then partial induction of FOX1 mRNA occurred upon g rowth to high cell density. A variety of mutants are known to affect t he glucose repression of many genes, including the FOX3 gene which enc odes the thiolase activity in peroxisomal beta oxidation. However, upo n examination none of these mutants showed de-repression of FOX1 expre ssion. Similarly we investigated the role of two inducers of genes enc oding peroxisomal enzymes (namely SNF1 and ADR1). No evidence was foun d to suggest that either of these plays a significant role in the indu ction of FOX1 mRNA levels. These observations indicate that the regula tion of FOX1 is under the control of as yet unidentified genes involve d in catabolite repression and suggest that the regulatory circuit inf luencing acyl CoA oxidase activity, and hence beta oxidation and perox isome function, is significantly different than that which might have been assumed from other studies.