Li R, Waga S, Hannon G J, Beach D, Stillman B
Cold Spring Harbor Laboratory, New York 11724.
Nature. 1994 Oct 6;371(6497):534-7. doi: 10.1038/371534a0.
In mammalian cells, DNA damage increases the levels of the nuclear tumour-suppressor p53, resulting in elevated synthesis of p21, an inhibitor of cyclin-dependent kinases (CDK). p21 may also directly block DNA replication by inhibiting the proliferating-cell nuclear antigen (PCNA), an essential DNA replication protein. However, PCNA is also required for nucleotide-excision repair of DNA, an intrinsic part of the cellular response to ultraviolet irradiation. Using an in vitro system, we now show that p21 does not block PCNA-dependent nucleotide-excision repair, in contrast to its inhibition of simian virus 40 DNA replication. Furthermore, the short gap-filling DNA synthesis by PCNA-dependent DNA polymerases delta and epsilon is less sensitive to inhibition by p21 than is long primer-extension synthesis. The ability of p21 to inhibit the role of PCNA in DNA replication but not in DNA repair rationalizes in vivo data showing that genetic damage leads to inactivation of chromosomal replication while allowing damage-responsive repair.
在哺乳动物细胞中，DNA损伤会增加核肿瘤抑制因子p53的水平，导致细胞周期蛋白依赖性激酶（CDK）抑制剂p21的合成增加。p21还可能通过抑制增殖细胞核抗原（PCNA）直接阻断DNA复制，PCNA是一种重要的DNA复制蛋白。然而，PCNA也是DNA核苷酸切除修复所必需的，这是细胞对紫外线照射反应的一个固有部分。我们现在利用体外系统表明，与p21抑制猿猴病毒40 DNA复制相反，它并不阻断PCNA依赖性核苷酸切除修复。此外，与长引物延伸合成相比，PCNA依赖性DNA聚合酶δ和ε进行的短缺口填充DNA合成对p21抑制的敏感性较低。p21抑制PCNA在DNA复制而非DNA修复中的作用，这一能力解释了体内数据，即遗传损伤导致染色体复制失活，同时允许损伤应答修复。
