MGA2 is involved in the low-oxygen response element-dependent hypoxic induction of genes in Saccharomyces cerevisiae

Eukaryotes have the ability to respond to changes in oxygen tension by alte rations in gene expression. For example, OLE1 expression in Saccharomyces c erevisiae is upregulated under hypoxic conditions. Previous studies have su ggested that the pathway regulating OLE1 expression by unsaturated fatty ac ids may involve Mga2p and Spt23p, two structurally and functionally related proteins. To define the possible roles of each of these genes on hypoxia-i nduced OLE1 expression, we examined OLE1 expression under normoxia, hypoxia , and cobalt treatment conditions in Delta mga2 or Delta spt23 deletion str ains. The results of OLE1 promoter-lacZ reporter gene and Northern blot ana lyses showed that hypoxia- and cobalt-induced OLE1 expression was dramatica lly decreased in a Delta mga2 strain but not in a Delta spt23 strain. Furth er analyses using low-oxygen response element (LORE)-CYC1-lacZ fusion repor ter assays and electrophoretic mobility shift assays (EMSAs) demonstrated t hat MGA2 significantly affects the LORE-dependent hypoxic induction pathway of gene expression. When MGA2 was supplied by a plasmid, the LORE-dependen t hypoxia-inducible reporter expression was recovered, as was the hypoxia-i nducible complex in EMSAs in the S. cerevisiae Delta mga2 strain. Supershif t analysis of EMSAs using crude extracts containing mycMga2p indicated that Mga2p is a component of the LORE-binding complex. Another LORE-dependent, hypoxia-inducible gene, ATF1, was similarly affected in the Delta mga2 stra in. These results indicate that MG42 is required for the LORE-dependent hyp oxic gene induction in S. cerevisiae.