High impact information on CHO2

• 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].
• The expression of INO1 RNA was also examined in cells containing a mutation (cho2) affecting the synthesis of phosphatidylcholine [2].
• Both biosynthetic enzymes were found to participate in the speciesselective methylation with Cho2p contributing the most [3].
• Phosphatidylethanolamine N-methyltransferase catalyzes the synthesis of phosphatidylcholine from phosphatidylethanolamine and is most active in liver [4].
• CHO 2, encoding human sterol 8-isomerase (hSI), was introduced into plasmids pYX213 or pET23a [5].

Biological context of CHO2

• 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 [6].
• In yeast, INO1 and CHO2 gene expression is subject to repression in response to inositol and choline supplementation [7].
• 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 [8].
• 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 [9].
• It has previously been shown that defects in phosphatidylcholine synthesis (cho2 and opi3) yield the Opi(-) phenotype because of a buildup of PA [10].

Anatomical context of CHO2

• Membranes of cho2 mutant cells grown in defined medium contain approximately 10% phosphatidylcholine (PC) and 40-50% PE as compared to wild-type levels of 40-45% PC and 15-20% PE [11].

Associations of CHO2 with chemical compounds

• The major effect on the levels of the CHO2 mRNA and OPI3 mRNA occurred in response to inositol [6].
• The addition of choline to inositol-containing growth medium repressed the levels of CHO2 mRNA and OPI3 mRNA abundance in wild-type cells [6].
• This analysis showed that the regulation of CHO2 mRNA and OPI3 mRNA abundance by inositol required phosphatidylcholine synthesis by the CDP-choline-based pathway [6].
• 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 [3].
• This activity could be distinguished from those remaining in the pem1 disruptant by its different pH optimum and apparent Km for S-adenosyl-L-methionine [8].

Regulatory relationships of CHO2

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

Other interactions of CHO2

• Sequence analysis established that the cDNA was not homologous to OPI3 or to CHO2, the only other yeast phospholipid N-methyltransferase, but was similar to several other classes of methyltransferases [13].
• A strain carrying the tightest of the three alleles was examined in detail and was found to express the set of co-regulated phospholipid structural genes (INO1, CHO1, CHO2 and OP13) constitutively [14].
• In order to investigate this regulation, we transformed wild-type yeast with a PEM1 promoter-lacZ fusion and isolated two mutants, named ric1 and ric2 (regulation by myo-inositol and choline), exhibiting decreased PEM1 expression [15].
• The majority of potential UASINO elements from the INO1 promoter were found to be inactive, whereas all of the elements from the CHO2 promoter tested were active [7].
• PS synthase expression was not depressed, while CDP-DG synthase and PI synthase expression decreased in cho2 and cho1 cells in the absence of inositol [16].

Analytical, diagnostic and therapeutic context of CHO2

• Molecular cloning of the yeast OPI3 gene as a high copy number suppressor of the cho2 mutation [12].

References