Transfer of GMP from the capping enzyme GT site to 5'-end of mRNA

The diphosphate 5'-end of the mRNA is joined to the GMP, releasing it from the enzyme. At this time, it is unclear how the RNA diphosphate end is transferred from the active site of the triphosphatase to the guanylyltransferase site. The covalent enzyme-GMP complex can form in the absence of RNA.<BR>Guanylyltransferase (GT) catalyzed second reaction can be represented as:ppN(pN)n + GTP -> GpppN(pN)n + PPi<P>
(Yamada-Okabe et al. 1998).

信使RNA的5'-端二磷酸基团与鸟苷酸（GMP）连接，从而将其从酶中释放。此时，RNA二磷酸基团的转移机制尚不明确，即从三磷酸酶的活性位点传递至鸟苷酸转移酶位点。即使在缺乏RNA的情况下，酶-鸟苷酸共价复合物亦能形成。鸟苷酸转移酶（GT）催化的第二反应可表示为：ppN(pN)n + GTP -> GpppN(pN)n + PPi（Yamada-Okabe 等人，1998年）。