title: Methylated nucleotides block 5' terminus of HeLa cell messenger RNA.
abstract: Polyadenylylated [poly(A)+] mRNA from HeLa cells that were labeled with [3H-methyl]-methionine and 14C-uridine was isolated by poly(U)-Sepharose chromatography. The presence of approximately two methyl groups per 1000 nucleotides of poly(A)+ RNA was calculated from the 3H/14C ratios and known degrees of methylation of 18S and 28S ribosomal RNAs. All four 2'-O-methylribonucleosides, but only two base-methylated derivatives, 7-methylguanosine (7MeG) and 6-methyladenosine (6MeA), were identified. 6MeA was the major component accounting for approximately 50% of the total methyl-labeled ribonucleosides. 7MeG, comprising about 10% of the total, was present exclusively at the 5' terminus of the poly(A)+ RNA and could be removed by periodate oxidation and beta elimination. Evidence for a 5' to 5' linkage of 7MeG to adjacent 2'-O-methylribonucleosides through at least two and probably three phosphates to give structures of the type 7MeG5'ppp5pNMep- and 7MeG5'ppp5'NMepNmep- was presented. The previous finding of similar sequences of methylated nucleotides in mRNA synthesized in vitro by enzymes associated with virus cores indicates that blocked 5' termini may be a characteristic feature of mRNAs that function in eucaryotic cells.
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000032:analysis; D000469:Alkaline Phosphatase / Q000378:metabolism; D001483:Base Sequence; D002250:Carbon Radioisotopes; D002848:Chromatography, DEAE-Cellulose; D002855:Chromatography, Thin Layer; D004586:Electrophoresis; D006151:Guanosine / Q000031:analogs & derivatives / Q000032:analysis; D006367:HeLa Cells / Q000032:analysis*; D006801:Humans; D006868:Hydrolysis; D008715:Methionine; D008745:Methylation; D009711:Nucleotides / Q000032:analysis*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis*; D012334:RNA, Neoplasm / Q000032:analysis*; D014316:Tritium; D014529:Uridine
chemical_list: D002250:Carbon Radioisotopes; D009711:Nucleotides; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D014316:Tritium; D006151:Guanosine; D008715:Methionine; D000469:Alkaline Phosphatase; D010727:Phosphoric Diester Hydrolases; D000241:Adenosine; D014529:Uridine