Isolation of the yeast structural gene for the membrane-associated enzyme phosphatidylserine synthase

The structural gene (CHO1) for phosphatidylserine synthase (CDPdiacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was isolated by genetic complementation in Saccharomyces cerevisiae from a bank of yeast genomic DNA on a chimeric plasmid. The cloned DNA (4.0 kilobases long) was shown to represent a unique sequence in the yeast genome. The DNA sequence on an integrative plasmid was shown to recombine into the CHO1 locus, confirming its genetic identity. The cho1 yeast strain transformed with this gene on an autonomously replicating plasmid had significantly increased activity of the regulated membrane-associated enzyme phosphatidylserine synthase. Partial purification of phosphatidylserine synthase from microsomes of this transformed strain confirmed that the membrane-bound enzyme was overproduced 6- to 7-fold as compared with the wild-type strain. The strain also synthesized the product phospholipid, phosphatidylserine, at an increased rate. The transformed strain had altered proportions of a variety of other phospholipids, suggesting that their synthesis is affected by the rate of synthesis of phosphatidylserine in yeast.