Mori H, Fukami Y, Haruna I
J Biochem. 1978 Sep;84(3):681-6. doi: 10.1093/oxfordjournals.jbchem.a132173.
Phage SP RNA-dependent RNA polymerase (SP replicase) was purified from Escherichia coli infected with RNA phage SP. The enzyme was found to be composed of four non-identical polypeptides, i.e. subunits I, II, III, and IV and molecular weights of 74,000, 69,000, 47,000, and 36,000 daltons, respectively. As in the case of phage Qbeta replicase, the largest polypeptide is identical with the ribosomal protein S1, and subunits III and IV with polypeptide chain elongation factors EF-Tu and EF-ts, respectively.. This is based on the behaviour of the subunits on SDS-polyacrylamide gel electrophoresis, isoelectric focusing and immunological cross-reaction. Subunits I, III, and IV of SP replicase are derived from the host cell, while subunit II is coded by phage RNA genome. The striking coincidence of the composition and entity of the structural components of SP replicase with those of Qbeta replicase may indicate the structural and functional requirements of host-derived polypeptides in RNA replicase. The binding activity of S1 (in 70S ribosome comples) to poly (U) is retained in SP replicase complex. In contrast, the GDP binding activity of EF-Tu is masked in SP replicase. It is concluded that S1 is required functionally whereas EF-Tu.EF-Ts are required structurally in RNA replicase.
噬菌体SP RNA依赖的RNA聚合酶（SP复制酶）是从感染了RNA噬菌体SP的大肠杆菌中纯化得到的。该酶由四种不同的多肽组成，即亚基I、II、III和IV，分子量分别为74,000、69,000、47,000和36,000道尔顿。与噬菌体Qβ复制酶的情况一样，最大的多肽与核糖体蛋白S1相同，亚基III和IV分别与多肽链延伸因子EF-Tu和EF-ts相同。这是基于亚基在SDS-聚丙烯酰胺凝胶电泳、等电聚焦和免疫交叉反应中的行为得出的。SP复制酶的亚基I、III和IV来自宿主细胞，而亚基II由噬菌体RNA基因组编码。SP复制酶与Qβ复制酶的结构成分在组成和实体上的惊人巧合可能表明RNA复制酶中宿主来源多肽的结构和功能要求。S1（在70S核糖体复合物中）与聚（U）的结合活性在SP复制酶复合物中得以保留。相反，EF-Tu的GDP结合活性在SP复制酶中被掩盖。可以得出结论，在RNA复制酶中，S1在功能上是必需的，而EF-Tu.EF-Ts在结构上是必需的。
