Barbie David A, Kudlow Brian A, Frock Richard, Zhao Jiyong, Johnson Brett R, Dyson Nicholas, Harlow Ed, Kennedy Brian K
Massachusetts General Hospital Cancer Center, Charlestown, MA 02129, USA.
Mol Cell Biol. 2004 Jan;24(2):595-607. doi: 10.1128/MCB.24.2.595-607.2004.
In primary mammalian cells, DNA replication initiates in a small number of perinucleolar, lamin A/C-associated foci. During S-phase progression in proliferating cells, replication foci distribute to hundreds of sites throughout the nucleus. In contrast, we find that the limited perinucleolar replication sites persist throughout S phase as cells prepare to exit the cell cycle in response to contact inhibition, serum starvation, or replicative senescence. Proteins known to be involved in DNA synthesis, such as PCNA and DNA polymerase delta, are concentrated in perinucleolar foci throughout S phase under these conditions. Moreover, chromosomal loci are redirected toward the nucleolus and overlap with the perinucleolar replication foci in cells poised to undergo cell cycle exit. These same loci remain in the periphery of the nucleus during replication under highly proliferative conditions. These results suggest that mammalian cells undergo a large-scale reorganization of chromatin during the rounds of DNA replication that precede cell cycle exit.
在原代哺乳动物细胞中，DNA复制起始于少数与核仁周围、核纤层蛋白A/C相关的位点。在增殖细胞的S期进程中，复制位点分布于整个细胞核的数百个位置。相比之下，我们发现，当细胞因接触抑制、血清饥饿或复制性衰老而准备退出细胞周期时，有限的核仁周围复制位点在整个S期持续存在。在这些条件下，已知参与DNA合成的蛋白质，如增殖细胞核抗原（PCNA）和DNA聚合酶δ，在整个S期都集中在核仁周围的位点。此外，染色体位点被重新导向核仁，并与准备退出细胞周期的细胞中的核仁周围复制位点重叠。在高度增殖条件下进行复制时，这些相同的位点仍保留在细胞核的外围。这些结果表明，哺乳动物细胞在退出细胞周期之前的DNA复制过程中经历了大规模的染色质重组。
