Viswanathan M, Dower K W, Lovett S T
Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02254-9110, USA.
J Biol Chem. 1998 Dec 25;273(52):35126-31. doi: 10.1074/jbc.273.52.35126.
RNase T was first identified as an enzyme responsible for end turnover of tRNA in Escherichia coli. Its activity, specific for tRNA-C-C-A, catalyzes the release of tRNA-C-C and AMP. RNase T, along with several other RNases, plays a role in maturation of several other RNA species by a similar limited nuclease activity. In previous work, we identified the gene for RNase T, rnt, as a high copy suppressor of the UV sensitivity conferred by deficiency in three single-strand DNA-specific exonucleases, RecJ, exonuclease I, and exonuclease VII. This suggested that RNase T may process DNA substrates as well. In this work, we show that purified RNase T possesses a potent 3' to 5' single-strand DNA-specific exonucleolytic activity. Its Km for single-strand DNA substrates is many orders of magnitude lower than that for tRNA, suggesting that single-strand DNA may be a natural biological substrate for RNase T. We suggest that the DNase activity of RNase T may play a role in end trimming reactions during DNA recombination and/or DNA repair.
核糖核酸酶T最初被鉴定为一种负责大肠杆菌中转运RNA（tRNA）末端周转的酶。它的活性对tRNA - C - C - A具有特异性，催化tRNA - C - C和AMP的释放。核糖核酸酶T与其他几种核糖核酸酶一起，通过类似的有限核酸酶活性在其他几种RNA种类的成熟过程中发挥作用。在之前的工作中，我们鉴定出核糖核酸酶T的基因rnt，它是由三种单链DNA特异性核酸外切酶RecJ、核酸外切酶I和核酸外切酶VII缺陷导致的紫外线敏感性的高拷贝抑制子。这表明核糖核酸酶T也可能处理DNA底物。在这项工作中，我们表明纯化的核糖核酸酶T具有强大的3'到5'单链DNA特异性核酸外切酶活性。它对单链DNA底物的Km值比对tRNA的Km值低许多个数量级，这表明单链DNA可能是核糖核酸酶T的天然生物学底物。我们认为核糖核酸酶T的脱氧核糖核酸酶活性可能在DNA重组和/或DNA修复过程中的末端修剪反应中起作用。
