CLONING OF A GENE (PSD1) ENCODING PHOSPHATIDYLSERINE DECARBOXYLASE FROM SACCHAROMYCES-CEREVISIAE BY COMPLEMENTATION OF AN ESCHERICHIA-COLI MUTANT

A gene (PSD1) encoding a phosphatidylserine decarboxylase of Saccharom yces cerevisiae was cloned by complementation of a conditional lethal mutation in the homologous gene in Escherichia coli strain EH150. Expr ession of the cDNA clone in EH150 corrected growth, phospholipid, and phosphatidylserine decarboxylase activity defects. Expression of the g enomic clone in wild type yeast resulted in 20-fold amplification of p hosphatidylserine decarboxylase activity. A 1500-base pair open readin g frame encodes a 56,558-Da protein with a potential mitochondrial tar geting sequence. Upstream regulatory elements found in other enzymes o f the phospholipid biosynthetic pathway are present in PSD1. The deriv ed amino acid sequence shows 44 and 35% identity with the phosphatidyl serine decarboxylases from Chinese hamster ovary cells and E. coli, re spectively. Near the carboxyl terminus is an LGST sequence which, in E . coli, is the site of proteolytic cleavage of the proenzyme into the alpha and beta subunits and formation of the pyruvate prosthetic group (Dowhan, W., and Li, Q.-X. (1992) Methods Enzymol. 209, 348-359). Dis ruption of the PSD1 gene in a haploid strain of yeast resulted in loss of detectable decarboxylase activity but little alteration of the gro wth properties or phospholipid composition. These results suggest that yeast has a second phosphatidylserine decarboxylation activity.