Synthesis of RNA containing a methylated blocked 5' terminus by HeLa nuclear homogenates

RNA synthesized in vitro by HeLa nuclei contains a variety of blocked methylated 5'-terminal structures that can be grouped into four general types: (a) m(7)GppN(m)p...; (b) m(7)GppN(m)pM(m)p...; (c) m(7)GpppN(m)p...; and (d) m(7)GpppN(m)pM(m).... Both N(m) and M(m) can be either one of the four 2'-O-methylated nucleosides. The relative amounts of the N(m) species are G = 45%, A = 25%, U = 20%, and C = 10%.