Ogawa T, Pickett G G, Kogoma T, Kornberg A
Proc Natl Acad Sci U S A. 1984 Feb;81(4):1040-4. doi: 10.1073/pnas.81.4.1040.
Escherichia coli rnh mutants defective in RNase H activity display the features of previously described sdrA (stable DNA replication) and dasF (dnaA suppressor) mutants: (i) sustained DNA replication in the absence of protein synthesis, (ii) lack of requirement for dnaA protein and the origin of replication (oriC), and (iii) sensitivity of growth to a rich medium. Both the sdrA mutants (selected for continued DNA replication in the absence of protein synthesis) and the dasF mutants (selected as dnaA suppressors) are defective in RNase H activity, measured in vitro. Furthermore, a 760-base-pair fragment containing the rnh+ structural gene complements the phenotype of each of the rnh, sdrA, and dasF mutants, indicative of a single gene. One function of RNase H in vivo is in the initiation of a cycle of DNA replication at oriC dependent on dnaA+. In keeping with these results, RNase H contributes to the specificity of dnaA protein-dependent replication initiated at oriC in a partially purified enzyme system.
核糖核酸酶H活性有缺陷的大肠杆菌rnh突变体表现出先前描述的sdrA（稳定DNA复制）和dasF（dnaA抑制子）突变体的特征：（i）在缺乏蛋白质合成的情况下持续进行DNA复制，（ii）对dnaA蛋白和复制起点（oriC）无需求，以及（iii）在丰富培养基中生长敏感。在体外测定中，sdrA突变体（在缺乏蛋白质合成时被选择用于持续DNA复制）和dasF突变体（被选择作为dnaA抑制子）的核糖核酸酶H活性均有缺陷。此外，包含rnh⁺结构基因的一个760碱基对片段可互补rnh、sdrA和dasF每个突变体的表型，表明是单个基因。核糖核酸酶H在体内的一个功能是在依赖dnaA⁺的情况下于oriC起始DNA复制循环。与这些结果一致，在一个部分纯化的酶系统中，核糖核酸酶H有助于在oriC起始的依赖dnaA蛋白的复制的特异性。
