IDENTIFICATION OF A CLASS OF SACCHAROMYCES-CEREVISIAE MUTANTS DEFECTIVE IN FATTY-ACID REPRESSION OF GENE-TRANSCRIPTION AND ANALYSIS OF THE FRM2 GENE

Exogenous fatty acids transcriptionally control the expression of a wi de variety of eukaryotic genes, many of which encode proteins involved in lipid metabolism. To identify gene products involved in the lipid signalling pathway, a reporter plasmid containing the 5'-upstream regi on of a gene demonstrated to be repressed by unsaturated fatty acids ( OLE1) was fused in frame to the Escherichia coli gene lac encoding bet a-galactosidase. Saccharomyces cerevisiae mutants defective in transcr iptional control by lipids were identified and this class of mutants h as been named Sim (fatty acid repression mutant). The mutants were org anized into six complementation groups designated frml-6. Mutants from two of the complementation groups, frm1 and frm3, were also defective in their ability to activate a reporter construct containing the 5'-u pstream region of POX1. POX1 has been shown to be transcriptionally ac tivated in the presence of unsaturated fatty acids. FRM2 was rescued b y a region of DNA localized to chromosome III. This region contained a n open reading frame of 579 nucleotides predicted to encode a M(r) 21 116 polypeptide. The upstream region of FRM2 contained a number of pot ential response elements which have previously been identified as impo rtant in regulating gene expression in response to glucose and certain fatty acids. Consistent with this observation, lacZ activity driven b y FRM2 or frm2 promoters was induced two- to three-fold dependent upon the carbon and fatty acid source utilized. The properties of FRM2 sug gest that it functions in the fatty acid signalling pathway and that i t is itself regulated by fatty acids.