Glover B P, McHenry C S
Department of Biochemistry, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
J Biol Chem. 2000 Feb 4;275(5):3017-20. doi: 10.1074/jbc.275.5.3017.
The DnaX complex subassembly of the DNA polymerase III holoenzyme is comprised of the DnaX proteins tau and gamma and the auxiliary subunits delta, delta', chi, and psi, which together load the beta processivity factor onto primed DNA in an ATP-dependent reaction. delta' and psi bind directly to DnaX whereas delta and chi bind to delta' and psi, respectively (Onrust, R., Finkelstein, J., Naktinis, V., Turner, J., Fang, L., and O'Donnell, M. (1995) J. Biol. Chem. 270, 13348-13357). Until now, it has been unclear which DnaX protein, tau or gamma, in holoenzyme binds the auxiliary subunits delta, delta', chi,and psi. Treatment of purified holoenzyme with the homobifunctional cross-linker bis(sulfosuccinimidyl)suberate produces covalently cross-linked gamma-delta' and gamma-psi complexes identified by Western blot analysis. Immunodetection of cross-linked species with anti-delta' and anti-psi antibodies revealed that no tau-delta' or tau-psi cross-links had formed, suggesting that the delta' and psi subunits reside only on gamma within holoenzyme.
DNA聚合酶III全酶的DnaX复合亚组件由DnaX蛋白tau和gamma以及辅助亚基delta、delta'、chi和psi组成，它们共同以ATP依赖反应将β持续合成因子加载到引发的DNA上。delta'和psi直接与DnaX结合，而delta和chi分别与delta'和psi结合（Onrust, R., Finkelstein, J., Naktinis, V., Turner, J., Fang, L., and O'Donnell, M. (1995) J. Biol. Chem. 270, 13348 - 13357）。到目前为止，尚不清楚全酶中的哪种DnaX蛋白，tau还是gamma，与辅助亚基delta、delta'、chi和psi结合。用同双功能交联剂双（磺基琥珀酰亚胺）辛二酸酯处理纯化的全酶会产生通过蛋白质免疫印迹分析鉴定的共价交联的gamma-delta'和gamma-psi复合物。用抗delta'和抗psi抗体对交联物种进行免疫检测表明，没有形成tau-delta'或tau-psi交联，这表明delta'和psi亚基仅存在于全酶中的gamma上。
