EXPRESSION IN YEAST OF AN ESCHERICHIA-COLI GENE ENCODING A PHOSPHOLIPID BIOSYNTHETIC ENZYME

Cardiolipin (CL) is a structurally unique phospholipid having importan t functional roles in both prokaryotic and eukaryotic cells. The genes encoding CL biosynthetic enzymes have been identified and extensively studied in Escherichia coli, and manipulation of CL biosynthesis in t his organism has elucidated a great deal about CL function in prokaryo tes. In contrast, little is known about CL biosynthesis or its regulat ion in eukaryotic cells. We sought to determine whether we could utili ze E. coli genes to manipulate expression of CL biosynthetic enzymes a nd CL content in yeast. The E. coli pgsA gene encodes phosphatidylglyc erophosphate synthase (PGPS), catalyzing the first step in the CL bios ynthetic pathway. We constructed plasmids with pgsA under the control of the yeast CUP1 promoter. Extracts of Saccharomyces cerevisiae cells transformed with this plasmid contained high levels of E. coli PGPS a ctivity. However, when compared to cells transformed with a control pl asmid, pgsA-transfonmed cells did not exhibit differences in phospholi pid composition. The most likely explanation is that the in vitro acti vity of the E. coli pgsA product is not indicative of its activity in vivo, due to mislocalization of the enzyme and/or inaccessibility of t he enzyme to the substrates. To our knowledge, this is the first demon stration of expression of a bacterial phospholipid biosynthetic enzyme in yeast.