title: 5'-Terminal 7-methylguanosine and mRNA function. The effect of enzymatic decapping and of cap analogs on translation of tobacco-mosaic-virus RNA and globin mRNA in vitro.
abstract: 1. Decapped tobacco mosaic virus (TMV) RNA and rabbit globin mRNA were prepared by enzymic treatment of RNAs with nucleotide pyrophosphatase purified from potato. The extent of removal of 5'-terminal 7-methylguanosine 5'-monophosphate (m7GMP) from TMV RNA was at least 97% as estimated by labeling of the 5' termini in vitro with S-adenosyl[methyl-3H]methionine catalysed by vaccinia virus methyltransferases. 2. The effect of enzymic decapping was compared with the effect of cap analogs on mRNAs translation in a nuclease-treated rabbit reticulocyte lysate and in a wheat germ extract. When translation was studied at low K+ concentration, little or no dependence on 5'-terminal 7-methylguanosine was found with either cell-free system. The importance of the 5'-terminal cap for the efficient translation of TMV RNA and globin mRNA increased as the concentration of K+ in a protein-synthesis system was raised. In a reticulocyte lysate analogs and enzymic decapping had a similar effect on translation. In a wheat germ extract, mRNA decapping resulted in a more pronounced decrease of mRNA activity, presumably due to the increased susceptibility of decapped mRNAs to the nucleases present in this protein synthesis system. 3. The requirement for a 5'-terminal cap was similar for the synthesis of 130,000-Mr and 165,000-Mr polypeptides coded by TMV RNA. This indicates that both proteins may be initiated at the common site close to the 5' terminus.
mesh_terms: D000818:Animals; D005914:Globins / Q000096:biosynthesis*; D006151:Guanosine / Q000031:analogs & derivatives* / Q000378:metabolism; D007700:Kinetics; D011188:Potassium / Q000494:pharmacology; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D014027:Tobacco Mosaic Virus / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D006151:Guanosine; C016578:7-methylguanosine; D005914:Globins; D011188:Potassium