High impact information on OPI3

• In cho2 and opi3 mutants, which are blocked in phosphatidylcholine synthesis, inositol-mediated repression of PGPS did not occur unless choline was added to the media [1].
• It was confirmed by Northern blotting that the level of INO1 and OPI3 gene transcripts, encoding key enzymes in phospholipid biosynthesis, were significantly elevated following treatment with Me2SO [2].
• The structural genes (PEM1 and PEM2) encoding the enzymes involved in the yeast phosphatidylethanolamine (PE) methylation pathway were cloned by means of genetic complementation using yeast mutants [3].
• Because of its rather broad substrate specificity, the enzyme encoded by PEM2 is designated as phospholipid methyltransferase [3].
• Finally, valproate, but not lithium, increases expression of phosphatidylcholine pathway genes CHO1 and OPI3 [4].

Biological context of OPI3

• Phosphatidylethanolamine methyltransferase (PEMT) and phospholipid methyltransferase (PLMT), which are encoded by the CHO2 and OPI3 genes, respectively, catalyze the three-step methylation of phosphatidylethanolamine to phosphatidylcholine in Saccharomyces cerevisiae [5].
• A mutant of a fourth locus, OPI3, does not synthesize I-1-P synthase constitutively, despite its inositol excretion phenotype [6].
• The results of nucleotide sequence analysis demonstrated that the coding frames of the PEM1 and PEM2 genes were capable of encoding 869- and 206-amino acid residues with calculated molecular weights of 101,202 and 23,150, respectively [3].
• We report the isolation of two new opi3 mutants by EMS mutagenesis, and construction of an insertion allele in vitro using the cloned gene [7].
• Promoter deletion analysis defined the 5' boundary of the regulatory region of PEM1 between -336 and -332 and that of PEM2 between -177 and -158 [8].

Anatomical context of OPI3

• We measured the lateral mobility of two fluorescent lipid probes dioctadecylindocarbocyanine (diI) and tetramethyl rhodamine phosphatidylethanolamine (R-PE) in the plasma membranes of Saccharomyces cerevisiae ino1 and opi3 spheroplasts [9].

Associations of OPI3 with chemical compounds

• The major effect on the levels of the CHO2 mRNA and OPI3 mRNA occurred in response to inositol [5].
• The addition of choline to inositol-containing growth medium repressed the levels of CHO2 mRNA and OPI3 mRNA abundance in wild-type cells [5].
• This analysis showed that the regulation of CHO2 mRNA and OPI3 mRNA abundance by inositol required phosphatidylcholine synthesis by the CDP-choline-based pathway [5].
• In the yeast Saccharomyces cerevisiae, the primary route for the biosynthesis of PC consists of three consecutive methylation steps of phosphatidylethanolamine (PE) catalyzed by the phospholipid N-methyltransferases Cho2p and Opi3p [10].
• It has previously been shown that defects in phosphatidylcholine synthesis (cho2 and opi3) yield the Opi(-) phenotype because of a buildup of PA [11].

Regulatory relationships of OPI3

• When present in multiple copies the OPI3 gene efficiently suppresses the phospholipid methylation defect of a cho2 mutation [12].

Other interactions of OPI3

• The mutant was identified by its disability to regulate expression of structural genes involved in phospholipid biosynthesis, INO1, CHO1 and OPI3, in response to supplementation with soluble lipid precursors [13].
• The regulation of CHO2 mRNA and OPI3 mRNA abundance generally correlated with the activities of PEMT and PLMT, respectively [5].

Analytical, diagnostic and therapeutic context of OPI3

• Molecular cloning of the yeast OPI3 gene as a high copy number suppressor of the cho2 mutation [12].
• Complementation test and spore analysis indicated that the disruptants were allelic with our previous mutants that were isolated by chemical mutagenesis and used for the cloning of PEM1 and PEM2 [14].

References