Dirksen M L, Crouch R J
J Biol Chem. 1981 Nov 25;256(22):11569-73.
Ordinarily, ribonuclease H hydrolyzes poly(rA) . poly(dT) and phiX174DNA-RNA at equal rates. Here we show that in the presence of dextran, the degradation of poly(rA) . poly(dT) is inhibited, while that of phi 174DNA-RNA is not. A similar inhibition by sucrose is found to be due to trace contamination of dextran in the sucrose. Ribose, deoxyribose, and a number of other saccharides fail to inhibit RNase H. In experiments where the two substrates are presented in the presence of the inhibitor, the kinetics indicates that both molecules are recognized by the enzyme, but only the phi X174DNA-RNA is degraded. That is, dextran does not interfere with the recognition site, but rather blocks hydrolysis. It is proposed that the ability of dextran to confer selectivity toward different substrates reveals a potential regulatory mechanism for RNase H activity which may represent a control step in the initiation of DNA synthesis.
通常情况下，核糖核酸酶H以相同速率水解聚（rA）·聚（dT）和φX174DNA-RNA。在此我们表明，在葡聚糖存在的情况下，聚（rA）·聚（dT）的降解受到抑制，而φ174DNA-RNA的降解则不受影响。发现蔗糖产生的类似抑制作用是由于蔗糖中存在痕量葡聚糖污染物。核糖、脱氧核糖以及许多其他糖类均不能抑制核糖核酸酶H。在抑制剂存在下同时加入两种底物的实验中，动力学表明两种分子均能被该酶识别，但只有φX174DNA-RNA被降解。也就是说，葡聚糖并不干扰识别位点，而是阻断水解。有人提出，葡聚糖赋予对不同底物选择性的能力揭示了核糖核酸酶H活性的一种潜在调控机制，这可能代表了DNA合成起始过程中的一个控制步骤。
