Isolation and characterization of ECT1 gene encoding CTP: phosphoethanolamine cytidylyltransferase of Saccharomyces cerevisiae

Saccharomyces cerevisiae mutants that were unable to utilize extracellular ethanolamine for phosphatidylethanolamine synthesis were isolated. Two of them carried recessive chromosomal mutations in a same gene and were defective in CTP:phosphoethanolamine cytidylyltransferase (ECT) activity in vitro (Ect- ). In an Ect- mutant that also carried the cho1 mutation, phosphatidylethanolamine accounted for less than 2% of total phospholipids, suggesting the importance of ECT in phosphatidylethanolamine synthesis. By screening a genomic library on a low copy number vector, three complementary clones of different size were isolated. A 2.8-kb common DNA region carried an open reading frame (ORF) of 969 bp in length, of which a truncated form failed to complement the Ect- mutation. This ORF was identical to the previously isolated MUQ1 gene of unknown function. Its deduced amino acid sequence had significant similarity to CTP:phosphocholine cytidylyltransferases of yeast and rat. The entire ORF, when combined with the glutathione S-transferase gene and expressed in Escherichia coli, exhibited ECT activity. These results indicate that the cloned gene encodes a catalytic subunit of ECT of S. cerevisiae.