MGA2 Is Involved in the Low-Oxygen Response Element-Dependent Hypoxic Induction of Genes in Saccharomyces cerevisiae

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Abstract
Eukaryotes have the ability to respond to changes in oxygen tension by alterations in gene expression. For example,OLE1 expression in Saccharomyces cerevisiae is upregulated under hypoxic conditions. Previous studies have suggested that the pathway regulating OLE1expression by unsaturated fatty acids may involve Mga2p and Spt23p, two structurally and functionally related proteins. To define the possible roles of each of these genes on hypoxia-inducedOLE1 expression, we examined OLE1expression under normoxia, hypoxia, and cobalt treatment conditions in Δmga2 or Δspt23 deletion strains. The results of OLE1promoter-lacZ reporter gene and Northern blot analyses showed that hypoxia- and cobalt-induced OLE1 expression was dramatically decreased in a Δmga2 strain but not in a Δspt23 strain. Further analyses using low-oxygen response element (LORE)-CYC1-lacZ fusion reporter assays and electrophoretic mobility shift assays (EMSAs) demonstrated that MGA2 significantly affects the LORE-dependent hypoxic induction pathway of gene expression. When MGA2 was supplied by a plasmid, the LORE-dependent hypoxia-inducible reporter expression was recovered, as was the hypoxia-inducible complex in EMSAs in the S. cerevisiae Δmga2 strain. Supershift 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 Δmga2 strain. These results indicate thatMGA2 is required for the LORE-dependent hypoxic gene induction in S. cerevisiae.