Flavell A J, Cowie A, Legon S, Kamen R
Cell. 1979 Feb;16(2):357-71. doi: 10.1016/0092-8674(79)90012-6.
Nuclear and cytoplasmic polyoma virus-specific RNA extracted from 32P-labeled mouse embryo cells late during productive viral infection was analyzed for the presence of 5' terminal capped structures by complete digestion with RNAases T1, T2 and A, followed by two-dimensional electrophoretic fractionation. Seven major cap I structures (m7 GpppNm1pN2p) were observed in both cases. These termini were further characterized by digestion with penicillium nuclease P1, followed by product analysis in a variety of alternative separate systems. Each structure had an individual combination of N1 and N2 nucleotides, where N1 was always a purine nucleotide but N2 was any nucleotide subject to the single exception that m7GpppGmpCp is found only in low yield. Four different cap II derivatives (m7GpppNm1pNm2pN3p) of four of the cap I structures were also detected in cytoplasmic RNA. None of the termini described derived from contaminating host cell RNA. All of these cap structures mapped on the polyoma viral DNA genome between 66 and 71 map units, a region distant from the 5' end of the bodies of two of the three late polyoma mRNAs. All the polyoma virus-specific cap structures, however, were present in each of the purified 16S, 18S and 19s late mRNAs. These data suggested that families of capped leader sequences of varying sizes are attached to the main body of each late polyoma mRNA species by a splicing mechanism.
从经32P标记的小鼠胚胎细胞在病毒生产性感染后期提取的核和细胞质多瘤病毒特异性RNA，通过用核糖核酸酶T1、T2和A完全消化，然后进行二维电泳分级分离，分析其5'末端帽状结构的存在情况。在两种情况下均观察到7种主要的帽I结构（m7GpppNm1pN2p）。通过用青霉核酸酶P1消化，然后在各种替代的分离系统中进行产物分析，对这些末端进行了进一步表征。每种结构都有N1和N2核苷酸的独特组合，其中N1总是嘌呤核苷酸，但N2可以是任何核苷酸，唯一的例外是m7GpppGmpCp的产量很低。在细胞质RNA中还检测到了4种帽I结构中的4种不同的帽II衍生物（m7GpppNm1pNm2pN3p）。所描述的末端均非来自污染的宿主细胞RNA。所有这些帽结构都定位在多瘤病毒DNA基因组的66至71个图谱单位之间，该区域距离三种晚期多瘤mRNA中两种的主体的5'端较远。然而，所有多瘤病毒特异性帽结构都存在于纯化的16S、18S和19S晚期mRNA的每一种中。这些数据表明，不同大小的带帽前导序列家族通过剪接机制连接到每种晚期多瘤mRNA物种的主体上。
