Analysis ofFAS3/ACCregulatory region ofSaccharomyces cerevisiae: identification of a functional UASINOand sequences responsible for fatty acid mediated repression

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Abstract
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 revealed that the UAS INO sequence at nucleotldes −719 to −710 is functional. The expression of FAS3-lacZ reporter genes and the measurement of mRNA levels in regulatory mutants of phospholipid biosynthesis clearly indicated that FAS3 is regulated by inositol and chollne. Previous studies have shown that the genes coding for fatty acid synthase, FAS1 and FAS2, are regulated by inositol (Chirala, S.S. [1992] Proc. Natl. Acad. Scl. USA 89,10232–10236). Thus all three genes involved In saturated fatty acid biosynthesis are coordlnately regulated with phospholipid biosynthesis. Comparison of the UAS IND sequences present in FAS1, FAS2 , and FAS3 suggested that the functional sequence of this UAS element Is YTTCACATG. However, even when the functional UAS IND was mutated, substantial expression of the FAS3-lacZ reporter gene was observed. Deletion analysis, electrophoretlc mobility shift assays, and expression using a heterologous reporter gene showed that the region between nucleotides −840 and −736 has two UAS elements. The same sequence seems to be responsible for fatty acld-medlated repression of FAS3 . The presence of these additional UAS sequences explains why yeast does not require fatty acids even when repressing amounts of inositol and choline are present In the medium.