FACTORS INFLUENCING GENETIC TRANSCRIPTION INITIATION AND TERMINATION

各种生物至少有一种酶能降解RNA-DNA杂交体的RNA。到目前为止，根据初级氨基酸序列的相似性，这些核糖核酸酶H(RNase H)可分为两类。从我们的研究中我们知道，具有良好特性的大肠杆菌RNaseHI在包括人和小鼠在内的许多不同物种中都有同源基因。我们知道，这些哺乳动物蛋白在序列和功能上与酿酒酵母的RNaseH1相似，除了RNaseH活性外，还具有双链RNA结合活性。酿酒酵母核糖核酸酶H1mRNA的合成在整个细胞周期中保持不变，而核糖核酸酶H2mRNA的合成在S和G2/M期最为丰富。双缺失突变菌株是可行的，但单一突变菌株对咖啡因和羟基脲的敏感性存在差异。在没有RNaseH1的情况下，RNA和RNaseH2(35)蛋白的水平增加。这些结果表明，RNaseH1参与了家务管理功能，清除了无意中形成的RNA-DNA杂交体，而RNaseH2参与了DNA复制和修复。-核糖核酸酶H，细胞周期，DNA复制，DNA修复

Various organisms have at least one enzyme that degrades the RNA of RNA-DNA hybrids. These ribonucleases H (RNases H), so far, fall into two classes based upon primary amino acid sequence similarity. From our studies, we know that the well- characterized Escherichia coli RNase HI has homologs in many different species including human and mouse. We know that these mammalian proteins resemble in sequence and function the RNase H1 of Saccharomyces cerevisiae by having a double- stranded RNA-binding activity in addition to the RNase H activity. Synthesis of mRNA for RNase H1 of S. cerevisiae is constant throughout the cell cycle whereas the mRNA for RNase H2 is most abundant at S and G2/M phase. Double-deletion mutant strains are viable yet there are diffferences in sensitivities of the single mutant strains to caffeine and hydroxyurea. The level of mRNA and RNase H2(35) protein increase in the absence of RNase H1. These results suggest that RNase H1 is involved in housekeeping function, removing inadvertently formed RNA-DNA hybrids while RNase H2 is involved in DNA replication and repair. - Ribonuclease H, cell cycle, DNA replication, DNA repair