| Abstract: | We have isolated two genes from yeast encoding 3-hydroxy-3-methylglutaryl-coenzyme A reductase hydroxymethylglutaryl-coenzyme A reductase (NADPH); HMG-CoA reductase; EC 1.1.1.34], the rate-limiting enzyme of sterol biosynthesis. These genes, HMG1 and HMG2, were identified by hybridization to a cDNA clone encoding hamster HMG-CoA reductase. DNA sequence analysis reveals homology between the amino acid sequence of the proteins encoded by the two yeast genes and the carboxyl-terminal half of the hamster protein. Cells containing mutant alleles of both HMG1 and HMG2 are unable to undergo spore germination and vegetative growth. However, cells containing a mutant allele of either HMG1 or HMG2 are viable but are more sensitive to compactin, a competitive inhibitor of HMG-CoA reductase, than are wild-type cells. Assays of HMG-CoA reductase activity in extracts from hmg1- and hmg2- mutants indicate that HMG1 contributes at least 83% of the activity found in wild-type cells. |
