Perry R P, Kelley D E, Friderici K, Rottman F
Cell. 1975 Apr;4(4):387-94. doi: 10.1016/0092-8674(75)90159-2.
An analysis of the methylated constituents of L cell mRNA by a combination of chromatographic methods and enzymatic treatments indicates that they comprise both 2'-O-methyl nucleosides and N6-methyl adenine, and/or 1-methyl adenine, and suggests that the 2'-O-methyl nucleotides, Ym, are part of an unusual class of sequences forming the 5' terminus of mRNA. These sequences seem to contain two 2'-O-methyl residues and a terminal residue that is not phosphorylated but, nevertheless, is blocked with respect to polynucleotid kinase reactivity. A strong candidate is a sequence of the type XppY1mpY2mpZp..., where X represents a blocking group which is itself occasionally methylated. The sequences isolated from total poly(A)+ mRNA contain all four species of 2'-O-methylated nucleoside, indicating some variability among different mRNA species. The methylated sequences do not appear to be enriched in the mRNA which hybridizes with repetitive DNA. The average L cell mRNA molecule also contains three residues of N6-methyl adenine. These residues are not part of the poly(A) segment, but appear to be located internal to the poly(A) near the 3' end of the mRNA molecules.
通过色谱方法和酶处理相结合对L细胞mRNA的甲基化成分进行分析表明，它们既包含2'-O-甲基核苷，也包含N6-甲基腺嘌呤和/或1-甲基腺嘌呤，并表明2'-O-甲基核苷酸Ym是构成mRNA 5'末端的一类特殊序列的一部分。这些序列似乎包含两个2'-O-甲基残基和一个末端残基，该末端残基未磷酸化，但在多核苷酸激酶反应性方面被封闭。一个强有力的候选序列是XppY1mpY2mpZp... 这种类型的序列，其中X代表一个本身偶尔会甲基化的封闭基团。从总poly(A)+ mRNA中分离出的序列包含所有四种2'-O-甲基化核苷，表明不同mRNA种类之间存在一定变异性。甲基化序列在与重复DNA杂交的mRNA中似乎并未富集。平均每个L细胞mRNA分子还含有三个N6-甲基腺嘌呤残基。这些残基不是poly(A)片段的一部分，而是似乎位于mRNA分子3'端附近的poly(A)内部。
