title: A B12-responsive internal ribosome entry site (IRES) element in human methionine synthase.
abstract: Regulation of homocysteine, a sulfur-containing amino acid that is a risk factor for cardiovascular diseases, is poorly understood. Methionine synthase (MS) is a key enzyme that clears intracellular homocysteine, and its activity is induced by its cofactor, vitamin B12, at a translational level. In this study, we demonstrate that translation of MS, which has a long and highly structured 5'-untranslated region, is initiated from an internal ribosome entry site (IRES), which is modulated by B12. The minimal IRES element spans 71 bases immediately upstream of the initiation codon. Electrophoretic mobility shift analysis reveals the presence of a B12 -dependent protein-RNA complex and suggests the possibility that B12-dependent increase of IRES efficiency is mediated via a protein. Modulation of the IRES-dependent translation of an essential gene by the cofactor of the encoded enzyme represents a novel example of a gene-nutrient interaction.
authors.affiliation: Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588-0664, USA.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Oltean
authors.forename: Ruma
authors.initials: R
authors.lastname: Banerjee
mesh_terms: D020121:5' Untranslated Regions; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000235:genetics*; D017398:Alternative Splicing; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002460:Cell Line; D002478:Cells, Cultured; D003062:Codon; D018387:Codon, Initiator; D003432:Cross-Linking Reagents / Q000494:pharmacology; D017353:Gene Deletion; D017930:Genes, Reporter; D006710:Homocysteine / Q000737:chemistry; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008957:Models, Genetic; D041681:NIH 3T3 Cells; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D014176:Protein Biosynthesis; D017433:Protein Structure, Secondary; D012313:RNA / Q000737:chemistry; D012270:Ribosomes / Q000648:ultrastructure*; D012307:Risk Factors; D014162:Transfection; D014805:Vitamin B 12 / Q000737:chemistry*
chemical_list: D020121:5' Untranslated Regions; D003062:Codon; D018387:Codon, Initiator; D003432:Cross-Linking Reagents; D006710:Homocysteine; D012313:RNA; D008156:Luciferases; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; D014805:Vitamin B 12