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.

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Journal Article | Research Support, U.S. Gov't, Non-P.H.S. | Research Support, U.S. Gov't, P.H.S.

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Lowry CV, Weiss JL, Walthall DA, Zitomer RS

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