A downstream regulatory element located within the coding sequence mediates autoregulated expression of the yeast fatty acid synthase gene FAS2 by the FAS1 gene product

The fatty acid synthase genes FAS1 and FAS2 of the: yeast Saccharomyces cer evisiae are transcriptionally, co-regulated by general transcription factor s (such as: Reb1, Rap1 and Abf1) and by the phospholipid-specific heterodim eric activator Ino2/Ino4, acting via their corresponding upstream binding s ites. Here we: provide evidence for a positive autoregulatory influence of FAS1 on FAS2 expression. Even with a constant FAS2 copy number, a 10-fold i ncrease of FAS2 transcript amount was observed in the presence of FAS1 in m ulti-copy, compared to a fas1 null mutant. Surprisingly, the first 66 nt of the FAS2 coding region turned out as necessary and sufficient for FAS1-dep endent gene expression. FAS2-lacZ fusion constructs deleted for this region showed high reporters gene expression even in the absence of FAS1, arguing for a negatively-acting downstream repression site (DRS) responsible for F AS1-dependent expression of FAS2. Our data suggest that the FAS1 gene produ ct, in addition to its catalytic function, is also required for the coordin ate biosynthetic control of the yeast FAS complex. An excess of uncomplexed Fas1 may be responsible for the deactivation of an FAS2-specific repressor , acting via the DRS.