Wei C M, Gershowitz A, Moss B
Cell. 1975 Apr;4(4):379-86. doi: 10.1016/0092-8674(75)90158-0.
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.
用[³H-甲基]-甲硫氨酸和¹⁴C-尿苷标记的HeLa细胞的聚腺苷酸化[poly(A)+]mRNA，通过聚(U)-琼脂糖凝胶柱层析进行分离。根据³H/¹⁴C比率以及18S和28S核糖体RNA已知的甲基化程度，计算出每1000个聚(A)+RNA核苷酸中大约有两个甲基。鉴定出了所有四种2'-O-甲基核糖核苷，但仅鉴定出两种碱基甲基化衍生物，即7-甲基鸟苷(7MeG)和6-甲基腺苷(6MeA)。6MeA是主要成分，约占总甲基标记核糖核苷的50%。7MeG约占总量的10%，仅存在于聚(A)+RNA的5'末端，可通过高碘酸盐氧化和β消除去除。提出了7MeG通过至少两个且可能三个磷酸与相邻的2'-O-甲基核糖核苷以5'至5'连接的证据，从而形成7MeG5'ppp5pNMep-和7MeG5'ppp5'NMepNmep-类型的结构。先前在与病毒核心相关的酶体外合成的mRNA中发现类似的甲基化核苷酸序列，这表明封闭的5'末端可能是在真核细胞中起作用的mRNA的一个特征。
