Graduate School of Life Science, University of Hyogo, Kamigori, Ako-gun, Hyogo, 678-1297, Japan.
Genes Cells. 2013 Nov;18(11):946-59. doi: 10.1111/gtc.12087. Epub 2013 Aug 13.
Proliferating cell nuclear antigen (PCNA) is loaded on chromatin upon initiation of the S phase and acts as a platform for a large number of proteins involved in chromosome duplication at the replication fork. As duplication is completed, PCNA dissociates from chromatin, and thus, chromatin-bound PCNA levels are regulated during the cell cycle. Although the mechanism of PCNA loading has been extensively investigated, the unloading mechanism has remained unclear. Here, we show that Elg1, an alternative replication factor C protein, is required for the regulation of chromatin-bound PCNA levels. When Elg1 was depleted by small interfering RNA, chromatin-bound PCNA levels were extremely increased during the S phase. The number of PCNA foci, regions in the nucleus normally representing DNA replication sites, was increased and PCNA remained on chromatin after DNA replication. Various chromatin-associated protein levels on chromatin were affected, and chromatin loop size was increased. During mitosis, cells with aberrant chromosomes and lagging chromosomes were frequently detected. Our findings suggest that Elg1 has an important role in maintaining chromosome integrity by regulating PCNA levels on chromatin, thereby acting as a PCNA unloading factor.
增殖细胞核抗原（PCNA）在 S 期开始时加载到染色质上，作为复制叉处涉及染色体复制的大量蛋白质的平台。当复制完成时，PCNA 从染色质上解离，因此，染色质结合的 PCNA 水平在细胞周期中受到调节。尽管已经广泛研究了 PCNA 的加载机制，但卸载机制仍不清楚。在这里，我们表明，替代复制因子 C 蛋白 Elg1 是调节染色质结合的 PCNA 水平所必需的。当 Elg1 被小干扰 RNA 耗尽时，染色质结合的 PCNA 水平在 S 期极度增加。PCNA 焦点（核内通常代表 DNA 复制位点的区域）的数量增加，并且 DNA 复制后 PCNA 仍留在染色质上。各种染色质相关蛋白的水平受到影响，染色质环的大小增加。在有丝分裂期间，经常检测到具有异常染色体和滞后染色体的细胞。我们的研究结果表明，Elg1 通过调节染色质上的 PCNA 水平在维持染色体完整性方面起着重要作用，因此它是一种 PCNA 卸载因子。
