Filipowicz W, Strugala K, Konarska M, Shatkin A J
Proc Natl Acad Sci U S A. 1985 Mar;82(5):1316-20. doi: 10.1073/pnas.82.5.1316.
RNA 3'-terminal phosphate cyclase has been partially purified from HeLa cells. In the presence of ATP and Mg2+, cyclase preparations catalyze conversion of RNA 3'-terminal phosphate to the 2',3'-cyclic phosphodiester. The mechanism of 3'-phosphate cyclization was studied with oligoribonucleotides containing terminal 2'-deoxy- or 2'-O-methylribose. Incubation of these substrates with cyclase and ATP results in formation of the corresponding activated 3'-terminal structures, dN(3')pp(5')A and Nm(3')pp(5')A. It is proposed that an intermediate step in cyclization is transfer of the adenylyl group from ATP to the 3' phosphate of RNA. Rapid attack of the adjacent 2'-OH normally follows, resulting in elimination of AMP and formation of the cyclic phosphodiester. Cyclase preparations can be covalently labeled with [alpha-32P]ATP, suggesting that an earlier step in the cyclization reaction involves formation of an adenylylated enzyme intermediate.
RNA 3'-末端磷酸环化酶已从人宫颈癌细胞（HeLa细胞）中部分纯化出来。在ATP和Mg2+存在的情况下，环化酶制剂可催化RNA 3'-末端磷酸转化为2',3'-环磷酸二酯。利用含有末端2'-脱氧核糖或2'-O-甲基核糖的寡核糖核苷酸研究了3'-磷酸环化的机制。将这些底物与环化酶和ATP一起温育会导致形成相应的活化3'-末端结构，即dN(3')pp(5')A和Nm(3')pp(5')A。有人提出环化过程中的一个中间步骤是腺苷酰基从ATP转移到RNA的3'-磷酸上。通常随后相邻的2'-OH会迅速进攻，导致AMP消除并形成环磷酸二酯。环化酶制剂可用[α-32P]ATP进行共价标记，这表明环化反应的较早步骤涉及形成腺苷酸化的酶中间体。
