Maki H, Kornberg A
Proc Natl Acad Sci U S A. 1987 Jul;84(13):4389-92. doi: 10.1073/pnas.84.13.4389.
The polymerase subunit (alpha) of Escherichia coli DNA polymerase III holoenzyme and the 3'----5' exonuclease subunit (epsilon) are each less active separately than together in the holoenzyme core (an assembly of alpha, epsilon, and theta subunits). In a complex formed from purified alpha and epsilon subunits, polymerase activity increased 2-fold, and that of the 3'----5' exonuclease increased 10- to 80-fold. The alpha-epsilon complex contains one each of the subunits as does the core. Stimulation of 3'----5' exonuclease activity is due mainly to a greatly increased affinity of the epsilon subunit for the 3'-hydroxyl terminus, resulting from DNA binding by the alpha subunit. Proofreading in the course of DNA synthesis by the alpha-epsilon complex was indistinguishable from that of the core. These findings identify the participation of the alpha subunit in proofreading by polymerase III holoenzyme and suggest that the fidelity of DNA replication may be influenced by the relative levels of the alpha and epsilon subunits in the cell.
大肠杆菌DNA聚合酶III全酶的聚合酶亚基（α）和3'→5'核酸外切酶亚基（ε）单独存在时的活性均低于它们在全酶核心（由α、ε和θ亚基组成的复合物）中的活性。在由纯化的α和ε亚基形成的复合物中，聚合酶活性增加了2倍，3'→5'核酸外切酶活性增加了10至80倍。α-ε复合物与核心一样，各含有一个亚基。3'→5'核酸外切酶活性的刺激主要是由于ε亚基对3'-羟基末端的亲和力大大增加，这是由α亚基与DNA结合导致的。α-ε复合物在DNA合成过程中的校对功能与核心的校对功能无法区分。这些发现确定了α亚基参与聚合酶III全酶的校对过程，并表明DNA复制的保真度可能受细胞中α和ε亚基相对水平的影响。
