Cloning and characterization of GPD2, a second gene encoding sn-glycerol 3-phosphate dehydrogenase (NAD +)in Saccharomyces cerevisiae, and its comparison with GPD1

We have cloned and characterized a homologue of the previously isolated GPD1 gene, encoding sn-glycerol 3-phosphate dehydrogenase (NAD +)in Saccharo- myces cerevisiae. This second gene, called GPD2, encodes a protein of 384 amino acids that shares 69 percent sequence identity with GPD1. Like GPD1 it has an amino-terminal extension of unknown function. GPD2 is located on chromosome VII and cross- hybridizes with GPD1 at chromosome IV as well as with an unknown homologue at chromosome XV. Dis- ruption of the GPD2 gene did not reveal any observ- able phenotypic effects, whereas overexpression resulted in a slight, but significant, increase of GPD enzyme activity in wild-type cells. Analysis of gene transcription by a CAT-reporter gene fused to the GPD promoters revealed decreased transcriptional activity of the GPD2 promoter in cells grown on non- fermentable as opposed to fermentable carbon sources, and no induction in cells exposed to high osmolarity or heat shock. Similar analysis of GPD1 demonstrated an 8-17-fold higher basal level of transcription compared to GPD2. Furthermore, such analysis revealed that the GPD1 promoter was induced by increased osmolarity essentially indepen- dent of the type of stress solute used, the level of GPD1 transcription being increased about sevenfold in cells growing at 1.4 M NaCI.