Nemer M, Surrey S, Ginzburg I, Echols M M
Nucleic Acids Res. 1979;6(6):2307-26. doi: 10.1093/nar/6.6.2307.
5' Terminal cap structures of hnRNA have been characterized and the extent of capping determined as a function of embryonic development. Sea urchin embryo hnRNA contains only the type-1 cap, m7GpppNmpNp, with the type-2 cap, which has a 2'-0-methylated subpenultimate nucleotide, being associated only with stable small nuclear RNAs. These cap 2-containing RNAs are synthesized at a rate of approximately 70 molecules min-1 nucleus-1 compared to approximately 1000 molecules for hnRNA cap 1. Approximately 70% of nuclear cap 1 is associated with greater than 15S RNA in denaturing solvent, but under non-denaturing conditions the percentage is much higher. Cap 1 in low and high molecular weight nuclear RNA have the same kinetics of methyl labeling. Thus all cap 1 structures may belong to a single class either covalent or H-bonded to high molecular weight RNA. hnRNA greater than 15S is 35% capped; however, adding caps in less than 15S RNA gives an estimate of 50% capping for total hnRNA. In development from early blastula to late gastrula, there is little if any change in the extent of capping of hnRNA. These results coupled with others indicate that the fraction of hnRNA molecules serving as precursor to mRNA does not change quantitatively during embryonic development.
核内不均一RNA（hnRNA）的5'末端帽结构已得到表征，并且帽化程度已被确定为胚胎发育的函数。海胆胚胎hnRNA仅含有1型帽，即m7GpppNmpNp，而2型帽（其倒数第二个核苷酸具有2'-O-甲基化）仅与稳定的小核RNA相关。与hnRNA帽1的约1000个分子相比，这些含帽2的RNA以约70个分子·分钟-1·核-1的速率合成。在变性溶剂中，约70%的核帽1与大于15S的RNA相关，但在非变性条件下，该百分比要高得多。低分子量和高分子量核RNA中的帽1具有相同的甲基标记动力学。因此，所有帽1结构可能属于与高分子量RNA共价或氢键结合的单一类别。大于15S的hnRNA有35%被加帽；然而，对小于15S的RNA加帽后，估计总hnRNA的加帽率为50%。在从早期囊胚到晚期原肠胚的发育过程中，hnRNA的加帽程度几乎没有变化（如果有变化也很小）。这些结果与其他结果表明，在胚胎发育过程中，作为mRNA前体的hnRNA分子比例在数量上没有变化。
