Arudchandran A, Cerritelli S, Narimatsu S, Itaya M, Shin D Y, Shimada Y, Crouch R J
Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2790, USA.
Genes Cells. 2000 Oct;5(10):789-802. doi: 10.1046/j.1365-2443.2000.00373.x.
RNA of RNA-DNA hybrids can be degraded by ribonucleases H present in all organisms including the eukaryote Saccharomyces cerevisiae. Determination of the number and roles of the RNases H in eukaryotes is quite feasible in S. cerevisiae.
Two S. cerevisiae RNases H, related to Escherichia coli RNase HI and HII, are not required for growth under normal conditions, yet, compared with wild-type cells, a double-deletion strain has an increased sensitivity to hydroxyurea (HU) and is hypersensitive to caffeine and ethyl methanesulphonate (EMS). In the absence of RNase H1, RNase H2 activity increases, and cells are sensitive to EMS but not HU and are more tolerant of caffeine; the latter requires RNase H2 activity. Cells missing only RNase H2 exhibit increased sensitive to HU and EMS but not caffeine
Mutant phenotypes infer that some RNA-DNA hybrids are recognized by both RNases H1 and H2, while other hybrids appear to be recognized only by RNase H2. Undegraded RNA-DNA hybrids have an effect when DNA synthesis is impaired, DNA damage occurs or the cell cycle is perturbed by exposure to caffeine suggesting a role in DNA replication/repair that can be either beneficial or detrimental to cell viability.
RNA-DNA杂交体中的RNA可被包括真核生物酿酒酵母在内的所有生物中存在的核糖核酸酶H降解。在酿酒酵母中确定真核生物中核糖核酸酶H的数量和作用是相当可行的。
与大肠杆菌核糖核酸酶HI和HII相关的两种酿酒酵母核糖核酸酶H在正常条件下生长不是必需的，然而，与野生型细胞相比，双缺失菌株对羟基脲（HU）的敏感性增加，并且对咖啡因和甲磺酸乙酯（EMS）超敏感。在没有核糖核酸酶H1的情况下，核糖核酸酶H2的活性增加，细胞对EMS敏感但对HU不敏感，并且对咖啡因更耐受；后者需要核糖核酸酶H2活性。仅缺失核糖核酸酶H2的细胞对HU和EMS的敏感性增加，但对咖啡因不敏感。
突变体表型推断一些RNA-DNA杂交体被核糖核酸酶H1和H2两者识别，而其他杂交体似乎仅被核糖核酸酶H2识别。当DNA合成受损、发生DNA损伤或细胞周期因接触咖啡因而受到干扰时，未降解的RNA-DNA杂交体具有影响，这表明其在DNA复制/修复中起作用，这对细胞活力可能是有益的或有害的。
