Identification and characterization of a low oxygen response element involved in the hypoxic induction of a family of Saccharomyces cerevisiae genes - Implications for the conservation of oxygen sensing in eukaryotes

An organism's ability to respond to changes in oxygen tension depends in la rge part on alterations in gene expression. The oxygen sensing and signalin g mechanisms in eukaryotic cells are not fully understood. To further defin e these processes, we have studied the Delta9 fatty acid desaturase gene OL E1 in Saccharomyces cerevisiae, We have confirmed previous data showing tha t the expression of OLE1 mRNA is increased in hypoxia and in the presence o f certain transition metals. OLE1 expression was also increased in the pres ence of the iron chelator 1,10-phenanthroline. A 142-base pair (bp) region 3' to the previously identified fatty acid response element was identified as critical for the induction of OLE1 in response to these stimuli using OL E1 promoter-lacZ reporter constructs. Electromobility shift assays confirme d the presence of an inducible band shift in response to hypoxia:a and coba lt. Mutational analysis defined the nonameric sequence ACTCAACAA as necessa ry for transactivation. A 20-base pair oligonucleotide containing this nona mer confers up regulation by hypoxia and inhibition by unsaturated fatty ac ids when placed upstream of a heterologous promoter in a lacZ reporter cons truct. Additional yeast genes were identified which respond to hypoxia and cobalt in a manner similar to OLE1. A number of mammalian genes are also up -regulated by hypoxia, cobalt, nickel, and iron chelators. Hence, the ident ification of a family of yeast genes regulated in a similar manner has impl ications for understanding oxygen sensing and signaling in eukaryotes.