Oxygen and haem regulate the synthesis of peroxisomal proteins: catalase A, acyl-CoA oxidase and Pex1p in the yeast Saccharomyces cerevisiae; the regulation of these proteins by oxygen is not mediated by haem

摘要

piSaccharomyces cerevisiae/i genes related to respiration are typically controlled by oxygen and haem. Usually the regulation by these factors is co-ordinated; haem is indicated as the oxygen sensor. However, the responsiveness of peroxisome functions to these regulatory factors is poorly understood. The expression of iCTA1/i, iPOX1/i and iPEX1/i genes encoding the peroxisomal proteins catalase A, acyl-CoA oxidase and Pex1p peroxin respectively was studied under various conditions: in anaerobiosis, in the absence of haem and in respiratory incompetence caused by the lack of a mitochondrial genome (ρsup0/sup). The influence of haem deficiency or ρsup0/sup on peroxisomal morphology was also investigated. Respiratory incompetence has no effect on the expression of iCTA1/i and iPOX1/i, whereas in the absence of haem their expression is markedly decreased. The synthesis of Pex1p is decreased in ρsup0/sup cells and is decreased even more in haem-deficient cells. Nevertheless, peroxisomal morphology in both these types of cell does not differ significantly from the morphology of peroxisomes in wild-type cells. The down-regulating effect of anoxia on the expression of iCTA1/i and iPOX1/i is even stronger than the effect of haem deficiency and is not reversed by the addition of exogenous haem or the presence of endogenous haem. Moreover, neither of these genes responds to the known haem-controlled transcriptional factor Hap1p. In contrast with the other two genes studied, iPEX1/i is up-regulated in anaerobiosis. The existence of one or more novel mechanisms of regulation of peroxisomal genes by haem and oxygen, different from those already known in iS. cerevisiae,/i is postulated./p