Burgers P M, Kornberg A
J Biol Chem. 1982 Oct 10;257(19):11474-8.
DNA polymerase III holoenzyme (holenzyme) has an ATPase activity elicited only by a primed DNA template. Reaction of preformed ATP.holoenzyme complex with a primed template results in hydrolysis of the ATP bound to the holoenzyme, release of ADP and Pi, and formation of an initiation complex between holoenzyme and the primed template. Approximately two ATP molecules are hydrolyzed for each initiation complex formed, a value in keeping with the number bound in the ATP.holoenzyme complex. The possibility that the latter and the initiation complex contain two holoenzyme molecules is supported by the presence of two beta monomers in the initiation complex. Holoenzyme action in the absence of ATP resembles that of pol III (the holoenzyme core) or DNA polymerase III (holoenzyme lacking the beta subunit), with or without ATP, in sensitivity to salt and in processivity of elongation. The initiation complex formed by ATP-activated holoenzyme resists a level of KCl (150 mM) that completely inhibits nonactivated holoenzyme and the incomplete forms of the holoenzyme, and displays a processivity at least 20 times greater. Upon completing replication of available template, holoenzyme can dissociate and form an initiation complex with another primed template, provided ATP is available to reactivate the holoenzyme. By inference, no essential subunits are lost in the cycle of initiation, elongation and dissociation.
DNA聚合酶III全酶仅由带引物的DNA模板引发具有ATP酶活性。预先形成的ATP·全酶复合物与带引物的模板反应会导致与全酶结合的ATP水解，释放出ADP和Pi，并在全酶与带引物的模板之间形成起始复合物。每形成一个起始复合物大约有两个ATP分子被水解，该值与ATP·全酶复合物中结合的ATP分子数一致。起始复合物中存在两个β单体支持了后者和起始复合物包含两个全酶分子的可能性。在没有ATP的情况下全酶的作用类似于pol III（全酶核心）或DNA聚合酶III（缺乏β亚基的全酶），无论有无ATP，在对盐的敏感性和延伸的持续合成能力方面都是如此。由ATP激活的全酶形成的起始复合物能抵抗一定水平的KCl（150 mM），而该水平的KCl会完全抑制未激活的全酶和全酶的不完全形式，并且其持续合成能力至少高出20倍。在完成对可用模板的复制后，只要有ATP可用于重新激活全酶，全酶就可以解离并与另一个带引物的模板形成起始复合物。由此推断，在起始、延伸和解离的循环中没有必需的亚基丢失。
