Podust V N, Podust L M, Goubin F, Ducommun B, Hübscher U
Department of Veterinary Biochemistry, University Zürich-Irchel, Switzerland.
Biochemistry. 1995 Jul 11;34(27):8869-75. doi: 10.1021/bi00027a039.
It is known that the direct binding of the cyclin-dependent kinase (Cdk) inhibitor p21, also called Cdk-interacting protein 1 (p21), to proliferating cell nuclear antigen (PCNA) results in the inhibition of PCNA-dependent DNA synthesis. We provide evidence that p21 first inhibits the replication factor C-catalyzed loading of PCNA onto DNA and second prevents the binding of DNA polymerase delta core to the PCNA clamp assembled on DNA. The second effect contributes most to the inhibition of pol delta holoenzyme activity. p21 primarily inhibited the DNA synthesis resulting from multiple reassembly of DNA polymerase delta holoenzyme. On the other hand, an ability of the PCNA clamp to translocate along double-stranded DNA was not affected by p21. These data were confirmed with a mutant of p21 that is unable to bind PCNA and therefore neither inhibited clamp assembly nor prevented the loading of DNA polymerase delta core onto DNA. Our data suggest that p21 does not discriminate in vitro "repair" and "replication" DNA synthesis based on template length but does act preferentially on polymerization which encounters obstacles to progress.
已知细胞周期蛋白依赖性激酶（Cdk）抑制剂p21，也称为Cdk相互作用蛋白1（p21），与增殖细胞核抗原（PCNA）的直接结合会导致PCNA依赖性DNA合成受到抑制。我们提供的证据表明，p21首先抑制复制因子C催化的PCNA加载到DNA上，其次阻止DNA聚合酶δ核心与组装在DNA上的PCNA钳位结合。第二种效应在抑制pol δ全酶活性中起主要作用。p21主要抑制由DNA聚合酶δ全酶多次重新组装导致的DNA合成。另一方面，PCNA钳位沿双链DNA移位的能力不受p21影响。这些数据通过p21的一个突变体得到证实，该突变体无法结合PCNA，因此既不抑制钳位组装，也不阻止DNA聚合酶δ核心加载到DNA上。我们的数据表明，p21在体外不会根据模板长度区分“修复”和“复制”DNA合成，但确实优先作用于遇到进展障碍的聚合反应。
