CLONING AND CHARACTERIZATION OF GPD2, A 2ND GENE ENCODING SN-GLYCEROL3-PHOSPHATE DEHYDROGENASE (NAD(-CEREVISIAE, AND ITS COMPARISON WITH GPD1()) IN SACCHAROMYCES)

We have cloned and characterized a homologue of the previously isolate d GPD1 gene, encoding sn-glycerol 3-phosphate dehydrogenase (NAD(+)) i n Saccharomyces cerevisiae. This second gene, called GPD2, encodes a p rotein of 384 amino acids that shares 69% sequence identity with GPD1. Like GPD1 it has an amino-terminal extension of unknown function. GPD 2 is located on chromosome VII and cross-hybridizes with GPD1 at chrom osome IV as well as with an unknown homologue at chromosome XV. Disrup tion of the GPD2 gene did not reveal any observable phenotypic effects , whereas overexpression resulted in a slight, but significant, increa se of GPD enzyme activity in wild-type cells. Analysis of gene transcr iption by a CAT-reporter gene fused to the GPD promoters revealed decr eased transcriptional activity of the GPD2 promoter in cells grown on nonfermentable as opposed to fermentable carbon sources, and no induct ion in cells exposed to high osmolarity or heat shock. Similar analysi s of GPD1 demonstrated an 8-17-fold higher basal level of transcriptio n compared to GPD2. Furthermore, such analysis revealed that the GPD1 promoter was induced by increased osmolarity essentially independent o f the type of stress solute used, the level of GPD1 transcription bein g increased about sevenfold in cells growing at 1.4 M NaCl.