title: Modulator sequences mediate oxygen regulation of CYC1 and a neighboring gene in yeast.
abstract: Three transcripts from Saccharomyces cerevisiae--CYC1 mRNA (transcribed from the iso-I cytochrome c gene) and two RNAs of unknown function, designated tr-1 and tr-2-were identified by reverse Southern blot analysis and found to be regulated in response to oxygen. CYC1 mRNA and tr-1 accumulation occurred only in the presence of oxygen while tr-2 appeared only under anaerobic conditions. tr-2 was transcribed from a region approximately 1 kilobase 5' from the CYC1 coding sequence and in the opposite direction. tr-1 showed homology to the same region as tr-2 but was transcribed from elsewhere in the genome. Expression of tr-2 and CYC1 was observed to be normal in cells transformed with centromeric plasmids carrying the two genes. Mutant transforming plasmids were constructed in which a 400-base-pair region between tr-2 and CYC1 was either deleted or inverted. The deletion led to low-level nearly unregulated expression of both the CYC1 and tr-2 genes, suggesting that sequences upstream from both genes are important for their expression and regulation. The inversion mutation produced a reversed pattern of CYC1 regulation in which the mRNA was present in anaerobically grown cells but absent in the presence of oxygen, mimicking wild-type tr-2 regulation and suggesting that the CYC1 transcription unit is under the control of the translocated tr-2 modulator sequences. Models for the function of these modulators are discussed.
mesh_terms: D003574:Cytochrome c Group / Q000031:analogs & derivatives* / Q000235:genetics; D045304:Cytochromes c; D005786:Gene Expression Regulation; D009876:Operon; D010100:Oxygen / Q000502:physiology*; D010957:Plasmids; D012333:RNA, Messenger / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D014158:Transcription, Genetic
chemical_list: C014059:CYC1 protein, S cerevisiae; D003574:Cytochrome c Group; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D045304:Cytochromes c; D010100:Oxygen