Lecomte P, Doubleday O P, Radman M
J Mol Biol. 1986 Jun 20;189(4):643-52. doi: 10.1016/0022-2836(86)90494-8.
The incorporation of exogenous deoxyribonucleotide monophates (dNMP) was measured under conditions of ongoing DNA synthesis, providing arguments for the existence of a [DNAn X dNMP X PPi] intermediate in the nucleotide incorporation step of DNA synthesis: (formula; see text). The existence of such an intermediate is suggested by an apparent exchange of both dNMP and pyrophosphate (PPi) moieties of the deoxyribonucleotide triphosphate (dNTP) substrate with exogenous molecules. Such exchange and the incorporation of exogenous dNMP into DNA, strictly require ongoing DNA synthesis, suggesting that the energy for exchange reactions is provided by the cleavage of dNTP substrate. We propose that nucleotide selection during ongoing DNA synthesis results largely from the different relative rates of forward (beta) and backward (-alpha) reactions involving the [DNAn X dNMP X PPi] intermediate: the forward (incorporation) reaction is expected to predominate for the correct nucleotide, whereas the backward (abortive) reaction is expected to predominate for incorrect nucleotides.
在外源脱氧核糖核苷酸单磷酸（dNMP）掺入的过程中，是在DNA持续合成的条件下进行测量的，这为DNA合成的核苷酸掺入步骤中存在[DNAn X dNMP X PPi]中间体提供了证据：（公式；见正文）。脱氧核糖核苷酸三磷酸（dNTP）底物的dNMP和焦磷酸（PPi）部分与外源分子之间明显的交换表明了这种中间体的存在。这种交换以及外源dNMP掺入DNA，严格要求DNA持续合成，这表明交换反应的能量是由dNTP底物的裂解提供的。我们提出，在DNA持续合成过程中的核苷酸选择主要源于涉及[DNAn X dNMP X PPi]中间体的正向（β）和反向（-α）反应的不同相对速率：对于正确的核苷酸，正向（掺入）反应预计占主导，而对于错误的核苷酸，反向（无效）反应预计占主导。
