Itaya M
Department of Molecular Biology, Mitsubishi Kasei Institute of Life Sciences, Tokyo, Japan.
Proc Natl Acad Sci U S A. 1990 Nov;87(21):8587-91. doi: 10.1073/pnas.87.21.8587.
An additional RNase H (EC 3.1.26.4), RNase HII, has been isolated from Escherichia coli K-12. By screening a library of E. coli DNA for clones that suppressed RNase H deficiency of an E. coli rnh mutant, a clone was obtained that produced a protein with RNase H activity. The overexpressed RNase HIII protein in E. coli was purified to near homogeneity and exhibited a strong preference for the ribonucleotide moiety of RNA-DNA hybrid as substrate. The terminal 11 amino acids were determined and were identical to those predicted from the nucleotide sequence. The rnhB gene, which encodes RNase HII, was distinct from rnhA by its map position (4.5 min on E. coli genetic map, between lpxB and dnaE) and by the lack of significant amino acid sequence similarity. The presence of a second RNase H in E. coli indicates that multiple RNase H genes per genome is a general feature of a general feature of a wide variety of organisms.
另一种核糖核酸酶H（EC 3.1.26.4），即核糖核酸酶HII，已从大肠杆菌K-12中分离出来。通过筛选大肠杆菌DNA文库以寻找能抑制大肠杆菌rnh突变体核糖核酸酶H缺陷的克隆，获得了一个能产生具有核糖核酸酶H活性蛋白质的克隆。在大肠杆菌中过表达的核糖核酸酶HIII蛋白被纯化至接近均一，并且对RNA-DNA杂交体的核糖核苷酸部分作为底物表现出强烈偏好。确定了其末端的11个氨基酸，与从核苷酸序列预测的氨基酸相同。编码核糖核酸酶HII的rnhB基因，在其图谱位置（在大肠杆菌遗传图谱上4.5分钟处，位于lpxB和dnaE之间）以及缺乏显著的氨基酸序列相似性方面，与rnhA不同。大肠杆菌中存在第二种核糖核酸酶H表明，每个基因组中有多个核糖核酸酶H基因是多种生物的一个普遍特征。
