Qiu J, Qian Y, Chen V, Guan M X, Shen B
Department of Cell and Tumor Biology, City of Hope National Medical Center and Beckman Research Institute, Duarte, California 91010, USA.
J Biol Chem. 1999 Jun 18;274(25):17893-900. doi: 10.1074/jbc.274.25.17893.
Yeast exonuclease 1 (Exo1) is induced during meiosis and plays an important role in DNA homologous recombination and mismatch correction pathways. The human homolog, an 803-amino acid protein, shares 55% similarity to the yeast Exo1. In this report, we show that the enzyme functionally complements Saccharomyces cerevisiae Exo1 in recombination of direct repeat DNA fragments, UV resistance, and mutation avoidance by in vivo assays. Furthermore, the human enzyme suppresses the conditional lethality of a rad27Delta mutant, symptomatic of defective RNA primer removal. The purified recombinant enzyme not only displays 5'-3' double strand DNA exonuclease activity, but also shows an RNase H activity. This result indicates a back-up function of exonuclease 1 to flap endonuclease-1 in RNA primer removal during lagging strand DNA synthesis.
酵母核酸外切酶1（Exo1）在减数分裂过程中被诱导，在DNA同源重组和错配修复途径中发挥重要作用。其人类同源物是一种803个氨基酸的蛋白质，与酵母Exo1有55%的相似性。在本报告中，我们通过体内实验表明，该酶在直接重复DNA片段的重组、紫外线抗性和避免突变方面在功能上补充了酿酒酵母Exo1。此外，人类酶抑制了rad27Delta突变体的条件致死性，这是RNA引物去除缺陷的症状。纯化的重组酶不仅具有5'-3'双链DNA核酸外切酶活性，还具有核糖核酸酶H活性。这一结果表明，在滞后链DNA合成过程中，核酸外切酶1在RNA引物去除方面对瓣状内切核酸酶-1具有备份功能。
