Oxygen regulation of anaerobic and aerobic genes mediated by a common factor in yeast.

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Abstract
The expression of a number of yeast genes is regulated by oxygen levels. While many of these are known to be induced in the presence of oxygen, a gene, ANB1, that responds in the opposite fashion, being expressed only under anaerobic conditions, was described. To identify genes involved in regulation of ANB1 and other oxygen-regulated genes, mutations causing constitutive expression of ANB1 were selected using a fusion of the ANB1 modulator segment to the CYC1 gene. A number of trans-acting mutations affecting a gene designated ROX1 caused constitutive expression of both the fused and wild-type genes, indicating that the ROX1 gene product operates through the ANB1 modulator seuqence at the level of transcription. The mutant alleles of ROX1 fall into 2 phenotypic classes. The rox1-a class is semi-dominant, and the rox1-b class is recessive. One mutant, rox1-a1, is pleiotropic and causes constitutive expression of 3 oxygen-induced genes.sbd.CYC1, SOD (superoxide dismutase) and tr-1 (an oxygen-induced gene with homology to ANB1).sbd.as well as constitutive expression of the oxygen-repressed ANB1 gene. Alleles of the rox1-b class cause constitutive expression of ANB1 but do not affect expression of the oxygen-induced genes tested. The pleiotropy of the rox1-a1 mutant indicates that the ROX1 gene product is involved in coordinate expression of both oxygen-induced and oxygen-repressed genes.