title: Transcriptional regulation of methionine synthase by homocysteine and choline in Aspergillus nidulans.
abstract: Roles played by homocysteine and choline in the regulation of MS (methionine synthase) have been examined in fungi. The Aspergillus nidulans metH gene encoding MS was cloned and characterized. Its transcription was not regulated by methionine, but was enhanced by homocysteine and repressed by choline and betaine. MS activity levels were regulated in a similar way. The repression by betaine was due to its metabolic conversion to choline, which was found to be very efficient in A. nidulans. Betaine and choline supplementation stimulated growth of leaky metH mutants apparently by decreasing the demand for methyl groups and thus saving methionine and S -adenosylmethionine. We have also found that homocysteine stimulates transcription of MS-encoding genes in Saccharomyces cerevisiae and Schizosaccharomyces pombe.
authors.affiliation: Department of Genetics, Institute of Biochemistry and Biophysics, PAS, Pawinskiego 5a, 02-106 Warsaw, Poland.
authors.forename: Magdalena M
authors.initials: MM
authors.lastname: Kacprzak
authors.forename: Irmina
authors.initials: I
authors.lastname: Lewandowska
authors.forename: Rowena G
authors.initials: RG
authors.lastname: Matthews
authors.forename: Andrzej
authors.initials: A
authors.lastname: Paszewski
mesh_terms: D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D001233:Aspergillus nidulans / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D001483:Base Sequence; D001622:Betaine / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology*; D003001:Cloning, Molecular; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D006710:Homocysteine / Q000494:pharmacology*; D008715:Methionine / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis; D014158:Transcription, Genetic
chemical_list: D012333:RNA, Messenger; D006710:Homocysteine; D001622:Betaine; D008715:Methionine; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; D002794:Choline