Snow E T, Foote R S, Mitra S
J Biol Chem. 1984 Jul 10;259(13):8095-100.
The kinetics of incorporation of deoxynucleotide precursors directed by the promutagenic base, O6-methylguanine (m6Gua), was analyzed during in vitro replication of m6Gua-containing synthetic polydeoxynucleotides by T4 and T5 phage DNA polymerases and Escherichia coli DNA polymerase I. When poly(dT,m6dG) and poly(dC,m6dG) with covalently attached primers were replicated, O6-methylguanine paired with either thymine or cytosine but with a much higher preference for thymine. dCTP and dTTP acted as competitive inhibitors of each other during DNA synthesis. O6-Methylguanine also directed incorporation of dAMP by T5 DNA polymerase. This dAMP incorporation was not inhibited by dTTP. Contrary to theoretical predictions that the m6dG X dT pair should be comparable to the dA X dT pair, the presence of m6dG in the template inhibited DNA synthesis. Based on Kappm values, E. coli DNA polymerase I showed a much higher preference for dTMP incorporation over dCMP opposite m6dG in the template than T4 and T5 DNA polymerases. At the same time, there was a higher turnover of dCTP than of dTTP by the E. coli enzyme. However, in all cases, the turnover of deoxynucleotides during replication of m6Gua-containing templates was more than that observed with templates without the alkylated base.
在由诱变前体碱基O6-甲基鸟嘌呤（m6Gua）指导的脱氧核苷酸前体掺入动力学过程中，通过T4和T5噬菌体DNA聚合酶以及大肠杆菌DNA聚合酶I对含m6Gua的合成多脱氧核苷酸进行体外复制时进行了分析。当共价连接引物的聚（dT，m6dG）和聚（dC，m6dG）被复制时，O6-甲基鸟嘌呤与胸腺嘧啶或胞嘧啶配对，但对胸腺嘧啶的偏好性更高。在DNA合成过程中，dCTP和dTTP相互作为竞争性抑制剂。O6-甲基鸟嘌呤还指导T5 DNA聚合酶掺入dAMP。这种dAMP掺入不受dTTP抑制。与m6dG×dT对应与dA×dT对相当的理论预测相反，模板中m6dG的存在抑制了DNA合成。基于Kappm值，与T4和T5 DNA聚合酶相比，大肠杆菌DNA聚合酶I在模板中m6dG对面掺入dTMP比掺入dCMP表现出更高的偏好性。同时，大肠杆菌酶对dCTP的周转比对dTTP的周转更高。然而，在所有情况下，含m6Gua模板复制过程中脱氧核苷酸的周转都比不含烷基化碱基的模板中观察到的周转更多。
