SELECTIVE-INHIBITION OF 3' TO 5' EXONUCLEASE ACTIVITY ASSOCIATED WITH DNA-POLYMERASES - MECHANISM OF MUTAGENESIS
SELECTIVE-INHIBITION OF 3' TO 5' EXONUCLEASE ACTIVITY ASSOCIATED WITH DNA-POLYMERASES - MECHANISM OF MUTAGENESIS
复制标题
DOI：
10.1021/bi00636a002
复制
发表时间：
1977-01-01
期刊：
影响因子：
2.9
通讯作者：
SO, AG
中科院分区：
文献类型：
--
作者：
BYRNES, JJ;DOWNEY, KM;SO, AG
与哺乳动物和细菌DNA聚合酶相关的3”至5”外切酶活性可以被5”-单磷酸核苷（包括6-巯基嘌呤- 5”-单磷酸核苷）选择性地抑制，但聚合酶活性不受影响。核苷、3′核苷酸和环核苷酸对外切酶活性没有影响。以聚（dA-dT）为模板/引物制备大肠杆菌DNA聚合酶I和哺乳动物DNA聚合酶。用非互补的核苷酸dGTP和dCTP催化三磷酸脱氧核糖核苷到单磷酸的模板依赖性转化。这表示非互补核苷酸在引物末端被聚合酶活性结合，随后被校对外切酶活性水解。选择性抑制外切酶活性导致游离dGMP或dCMP的产生减少，而dGMP或dCMP结合到poly（dA-dT）中的量增加，从而导致更高的错误频率。6-巯基嘌呤是一种已知的大肠杆菌诱变剂，它的衍生物硫唑嘌呤是鼠伤寒沙门氏菌的诱变剂，也是人类的致癌物。硫唑嘌呤在体内很容易转化为6-巯基嘌呤。6-巯基嘌呤和硫唑嘌呤对微生物的致突变性和对人体的致癌性可能是由于6-巯基嘌呤的活性代谢产物- 6-巯基嘌呤核糖核苷5′-单磷酸选择性抑制与DNA聚合酶相关的校对外切酶。这将导致更高频率的错配碱基在DNA和随之而来的突变。
The 3'' to 5'' exonuclease activity associated with mammalian and bacterial DNA polymerases can be selectively inhibited by nucleoside 5''-monophosphates including 6-mercaptopurine ribonucleoside 5''-monophosphate, but the polymerase activity is not affected. Nucleosides, 3'' nucleotides and cyclic nucleotides have no effect on exonuclease activity. With poly(dA-dT) as a template/primer Escherichia coli DNA polymerase I and mammalian DNA polymerase .delta. catalyze the template-dependent conversion of deoxyribonucleoside triphosphate to monophosphate with the noncomplementary nucleotides dGTP and dCTP. This represents the incorporation of the noncomplementary nucleotide at the primer terminus by the polymerase activity and its subsequent hydrolysis by the proofreading exonuclease activity. Selective inhibition of the exonuclease activity results in a decrease in the amount of free dGMP or dCMP generated and an increase in the amount of dGMP or dCMP incorporated into poly(dA-dT), and, thus, to a higher error frequency. 6-Mercaptopurine is a known mutagen in E. coli and its derivative, Azathioprine, is a mutagen in Salmonella typhimurium and a carcinogen in man. Azathioprine is readily converted to 6-mercaptopurine in vivo. The mutagenicity of 6-mercaptopurine and Azathioprine in microorganisms and their carcinogenicity in man are probably due to the selective inhibition of the proofreading exonuclease associated with DNA polymerases by 6-mercaptopurine ribonucleoside 5''-monophosphate, the active metabolite of 6-mercaptopurine. This would result in a higher frequency of mispaired bases in DNA and consequent mutation.