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The phospholipid methyltransferases in yeast
1Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Biochimica Et Biophysica Acta
|November 25, 1997
Summary
Two enzymes, phospholipid N-methyltransferases (PLMTs), are crucial for phosphatidylcholine (PC) synthesis in yeast. Both class I and class II PLMTs are essential for optimal growth in Schizosaccharomyces pombe, highlighting their importance in fungal lipid metabolism.
Area of Science:
- Biochemistry
- Molecular Biology
- Yeast Genetics
Background:
- Phosphatidylcholine (PC) synthesis in yeast involves two key enzymes: class I and class II phospholipid N-methyltransferases (PLMTs).
- Class II PLMTs catalyze the initial methylation of phosphatidylethanolamine (PE) to phosphatidyl-monomethylethanolamine (PMME).
- Class I PLMTs perform the subsequent two methylation steps, converting PMME to PC, and are homologous to mammalian PEMT.
Purpose of the Study:
- To investigate the roles of class I and class II PLMTs in the biosynthesis of PC in Saccharomyces cerevisiae and Schizosaccharomyces pombe.
- To compare the functional requirements and regulatory mechanisms of these enzymes in two distinct yeast species.
- To understand the genetic basis for PC synthesis and its regulation in fungi.
Main Methods:
- Gene cloning and characterization of class I and class II PLMTs from S. cerevisiae and S. pombe.
- Construction and analysis of yeast deletion mutants lacking specific PLMT genes.
- Phenotypic analysis of mutant strains, including growth assays in the absence of choline and measurement of PC levels.
- Investigation of gene expression regulation in response to precursors and growth phase.
Main Results:
- Deletion of either class II or class I PLMT in S. cerevisiae leads to slow growth and reduced PC levels without choline.
- Mutants of S. pombe lacking either PLMT are auxotrophic for choline, indicating essential roles for both enzymes.
- The S. cerevisiae class I enzyme demonstrates the capacity to catalyze all three methylation steps to PC.
- S. cerevisiae PLMT genes are transcriptionally regulated by inositol, choline, and growth phase.
- S. pombe PLMT regulation appears to be post-transcriptional concerning choline availability, with transcriptional regulation by growth phase.
Conclusions:
- Both class I and class II PLMTs are vital for efficient PC biosynthesis in yeast, with differing dependencies observed between S. cerevisiae and S. pombe.
- The S. cerevisiae class I enzyme possesses broader catalytic activity than initially proposed for class II enzymes.
- Differential regulatory mechanisms at transcriptional and post-transcriptional levels govern PLMT gene expression in response to nutrient availability and growth conditions in yeast.