Williams A J, Wernette C M, Kaguni L S
Department of Biochemistry, Michigan State University, East Lansing 48824.
J Biol Chem. 1993 Nov 25;268(33):24855-62.
Mitochondrial DNA polymerase from Drosophila embryos has been characterized with regard to its mechanism of DNA synthesis under the influence of a variety of compounds in moderate salt (120 mM KCl), where the enzyme is most highly active and only moderately processive, and in low salt (30 mM KCl), where it is less active yet most highly processive. Disparate activity and processivity optima were obtained in low salt in the presence of varying pH or MgCl2 and ATP concentrations; in moderate salt, optimal activity and processivity were achieved coincidentally. Whereas no correlation between processivity and activity optima was observed upon addition of polyethylene glycol in either low or moderate salt, the optima were coincident at both salt levels on addition of glycerol. None of the reaction conditions examined allowed DNA polymerase gamma to exhibit maximal activity and processivity concurrently; maximal activity was always achieved in moderate salt and the highest processivity in low salt. However, while limiting the availability of primer termini had no effect on the mechanism of DNA synthesis, we found that the ability of mitochondrial DNA polymerase to copy singly primed M13 DNA was enhanced then diminished during the course of purification, suggesting loss of an accessory factor.
果蝇胚胎中的线粒体DNA聚合酶已在中等盐浓度（120 mM KCl）和低盐浓度（30 mM KCl）条件下，针对其在多种化合物影响下的DNA合成机制进行了表征。在中等盐浓度下，该酶活性最高但持续性一般；在低盐浓度下，其活性较低但持续性最高。在低盐条件下，改变pH值、MgCl₂和ATP浓度会得到不同的活性和持续性最佳值；在中等盐浓度下，最佳活性和持续性同时出现。在低盐或中等盐条件下添加聚乙二醇时，未观察到持续性和活性最佳值之间的相关性，但添加甘油时，两种盐浓度下的最佳值均一致。所研究的反应条件均无法使DNA聚合酶γ同时展现出最大活性和持续性；最大活性总是在中等盐浓度下实现，而最高持续性则在低盐浓度下实现。然而，虽然限制引物末端的可用性对DNA合成机制没有影响，但我们发现线粒体DNA聚合酶复制单引物M13 DNA的能力在纯化过程中先增强后减弱，这表明一种辅助因子丢失了。
