Heme-regulated expression of two yeast acyl-CoA:sterol acyltransferases is involved in the specific response of sterol esterification to anaerobiosis.

Sterol esterification in Saccharomyces cerevisiae is catalyzed by two acyl-CoA:sterol acyltransferases encoded by the genes ARE1 and ARE2. Using double mutants in the HEM1 gene and individual ARE genes we demonstrated that the relative contribution of these two enzymes to sterol esterification was dependent on cellular heme status. Observed changes in sterol esterification could be explained by a different effect of heme on the transcription of both genes: while the ARE1 transcript level was elevated in heme-deficient and anaerobic cells, the ARE2 gene transcript was more abundant in aerobic cells competent for heme synthesis. Our results indicate that transcriptional regulation of ARE genes by heme and specific substrate preferences of Are1p and Are2p may be involved in the adaptation of yeast sterol metabolism to hypoxia.