ANALYSIS OF FAS3 ACC REGULATORY REGION OF SACCHAROMYCES-CEREVISIAE - IDENTIFICATION OF A FUNCTIONAL UAS(INO) AND SEQUENCES RESPONSIBLE FOR FATTY-ACID MEDIATED REPRESSION/

We have determined the sequence of the FAS3/ACC regulatory region and mapped the transcription initiation site. In this sequence, there are two putative UAS(INO) sequences. Deletion and mutational analyses reve aled that the UAS(INO) sequence at nucleotides -719 to -710 is functio nal. The expression of FAS3-lacZ reporter genes and the measurement of mRNA levels in regulatory mutants of phospholipid biosynthesis clearl y indicated that FAS3 is regulated by inositol and choline. Previous s tudies have shown that the genes coding for fatty acid synthase, FAS1 and FAS2, are regulated by inositol (Chirala, S.S. [1992] Proc. Natl. Acad. Sci. USA 89, 10232-10236). Thus all three genes involved in satu rated fatty acid biosynthesis are coordinately regulated with phosphol ipid biosynthesis. Comparison of the UAS(INO) sequences present in FAS 1, FAS2, and FAS3 suggested that the functional sequence of this UAS e lement is YTTCACATG. However, even when the functional UAS(INO) was mu tated, substantial expression of the FAS3-lacZ reporter gene was obser ved. Deletion analysis, electrophoretic mobility shift assays, and exp ression using a heterologous reporter gene showed that the region betw een nucleotides -840 and -736 has two UAS elements. The same sequence seems to be responsible for fatty acid-mediated repression of FAS3. Th e presence of these additional UAS sequences explains why yeast does n ot require fatty acids even when repressing amounts of inositol and ch oline are present in the medium.