Kogoma T, Subia N L, von Meyenburg K
Mol Gen Genet. 1985;200(1):103-9. doi: 10.1007/BF00383320.
Escherichia coli rnh mutants lacking ribonuclease H (RNase H) activity can tolerate deletion of the origin of DNA Replication (delta oriC) and transposon-insertional inactivation of an initiator gene (dnaA::Tn10). Introduction of the recA200 allele encoding a thermolabile RecA protein into rnh- dnaA::Tn10 and rnh- delta oriC mutants strains rendered DNA synthesis and colony formation of these mutants temperature sensitive. The temperature sensitivity and the broth sensitivity (Srm-) of the rnh- dnaA::Tn10 recA200 strain was suppressed by the presence of plasmids (pBR322 derivatives) carrying dnaA+ only when the intact oriC site was present on the chromosome. Lack of RNase H activity neither promoted replication of minichromosomes (pOC24 and p lambda asn20) in the absence of required DnaA+ protein nor inhibited dnaA+-dependent minichromosome replication. These results led to the conclusion that RNase H is not directly involved in the events leading to initiation of DNA replication at oriC. Rather, it functions as a specificity factor by eliminating certain forms of RNA-DNA hybrids which could otherwise be used to prime DNA replication at sites other than oriC.
缺乏核糖核酸酶H（RNase H）活性的大肠杆菌rnh突变体能够耐受DNA复制起点（delta oriC）的缺失以及引发基因（dnaA::Tn10）的转座子插入失活。将编码热不稳定RecA蛋白的recA200等位基因导入rnh- dnaA::Tn10和rnh- delta oriC突变体菌株后，这些突变体的DNA合成和菌落形成变得对温度敏感。只有当完整的oriC位点存在于染色体上时，携带dnaA+的质粒（pBR322衍生物）才能抑制rnh- dnaA::Tn10 recA200菌株的温度敏感性和肉汤敏感性（Srm-）。在缺乏所需的DnaA+蛋白时，RNase H活性的缺失既不促进微型染色体（pOC24和p lambda asn20）的复制，也不抑制依赖dnaA+的微型染色体复制。这些结果得出结论，RNase H并不直接参与导致在oriC处启动DNA复制的事件。相反，它通过消除某些形式的RNA-DNA杂交体发挥特异性因子的作用，否则这些杂交体可用于在oriC以外的位点引发DNA复制。
