Transcriptional regulation of YML083c under aerobic and anaerobic conditions

YML083c and DAN1 were among the Saccharomyces cerevisiae ORFs that displayed the strongest increase in transcript abundance during anaerobic growth compared to aerobic growth, as determined by oligonucleotide microarrays. We here report that transcription of YML083c is regulated by at least three different factors. First, repression under aerobic conditions depends on the presence of heme. Second, deletion analysis of the 5'-flanking region of YML083c and DAN1 revealed two regions responsible for anaerobic induction. Each of these regions conferred anoxia-regulated expression to the heterologous, minimal, CYC1-lacZ reporter. Mutations in the AAACGA subelement, common to the positive acting regions of YML083c and DAN1, almost completely abolished the ability to drive anaerobic expression of the reporter gene. This subelement is similar to the AR1 site, which is involved in anaerobic induction of the DAN/TIR genes. Activation through the AR1 site depends on Upc2. Indeed, transcription from the YML083c promoter was decreased in an upc2 null mutant. Third, expression of Sut1 under aerobic conditions enhanced transcription of YML083c, suggesting that aerobic repression of YML083c is promoted by the general Tup1-Ssn6 co-repressor complex. However, despite the presence of a sequence that matches the consensus for binding of Rox1, YML083c is not controlled by Rox1, since deletion or replacement of the putative binding site did not cause aerobic derepression. Moreover, YML083c expression was undetectable in aerobically grown cells of a rox1 null mutant.