Shuman S, Hurwitz J
Proc Natl Acad Sci U S A. 1981 Jan;78(1):187-91. doi: 10.1073/pnas.78.1.187.
Vaccinia virus RNA guanylyltransferase catalyzes the transfer of GMP from GTP to the 5'-triphosphate or diphosphate terminus of RNA to generate the cap structure G(5')ppp(5')N-. The guanylylation reaction consists of a series of at least two partial reactions: (i) GTP + E in equilibrium E-pG + PPi, (ii) E-pG + (p)ppNpNpN- leads to GpppNpNpN- + E. Inthe first of these, GTP reacts with capping enzyme in the absence of an RNA acceptor to form a covalent enzyme-guanylate intermediate. The GMP is linked to the Mr 95,000 subunit of the capping enzyme via a phosphoamide bond, as judged by the acid-labile, alkali-stable nature of the bond and by the susceptibility of the linkage to cleavage by hydroxylamine at pH 4.75. The isolated enzyme-guanylate complex is able to transfer the guanylate moiety to triphosphate-terminated poly(A) to yield the 5' cap structure GpppA or to pyrophosphate to regenerate GTP. Both partial reactions of transguanylylation require a divalent cation.
痘苗病毒RNA鸟苷酸转移酶催化GMP从GTP转移至RNA的5'-三磷酸或二磷酸末端，以生成帽结构G(5')ppp(5')N-。鸟苷酸化反应由一系列至少两个部分反应组成：(i) GTP + E ⇌ E-pG + PPi，(ii) E-pG + (p)ppNpNpN- → GpppNpNpN- + E。在第一个反应中，GTP在没有RNA受体的情况下与加帽酶反应，形成共价的酶-鸟苷酸中间体。根据该键对酸不稳定、对碱稳定的性质以及该连接在pH 4.75下对羟胺裂解的敏感性判断，GMP通过磷酰胺键与加帽酶的95,000 Mr亚基相连。分离得到的酶-鸟苷酸复合物能够将鸟苷酸部分转移至三磷酸末端的聚(A)以产生5'帽结构GpppA，或者转移至焦磷酸以再生GTP。转鸟苷酸化的两个部分反应均需要二价阳离子。
