CDC28 phosphorylates Cac1p and regulates the association of chromatin assembly factor i with chromatin
CDC28 phosphorylates Cac1p and regulates the association of chromatin assembly factor i with chromatin
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DOI：
10.4161/15384101.2014.973745
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发表时间：
2015-01-01
期刊：
影响因子：
4.3
通讯作者：
Yankulov, Krassimir
中科院分区：
文献类型：
--
作者：
Jeffery, Daniel C. B.;Kakusho, Naoko;Yankulov, Krassimir
染色质组装因子I（Chromatin Assembly Factor I，CAF-I）在核小体的复制偶联组装过程中起关键作用。预计其功能与细胞周期的调节有关，但详细信息很少。目前的模型表明，CAF-I是通过其Cac 1 p亚基和复制滑动钳，PCNA之间的相互作用，招募到复制叉和染色质，这种相互作用是由激酶CDC 7刺激。在这里，我们表明，另一种激酶，CDC 28，磷酸化Cac 1 p的丝氨酸94和515在早期S期，并调节其与染色质的关联，但不与PCNA的关联。突变的Cac 1 p磷酸化位点的CDC 28，而不是CDC 7实质上减少体内磷酸化的Cac 1 p。然而，Cac 1 p上推定的CDC 7靶位点的突变降低了其稳定性。CAF-I与染色质的结合在cdc 28 -1突变体中受损，在cdc 7 -1突变体中受损程度较小。此外，CDC 28和CDC 7在Cac 1 p磷酸化位点的突变减少了端粒的基因沉默。我们认为，这种磷酸化代表了CAF-I在早期S期向染色质募集的调节步骤，这与CAF-I与PCNA的关联不同。因此，我们暗示CDC 28在DNA复制过程中的染色质重组的调节。这些发现为细胞周期调控、DNA复制和染色质重组之间的联系提供了新的机制见解。
Chromatin Assembly Factor I (CAF-I) plays a key role in the replication-coupled assembly of nucleosomes. It is expected that its function is linked to the regulation of the cell cycle, but little detail is available. Current models suggest that CAF-I is recruited to replication forks and to chromatin via an interaction between its Cac1p subunit and the replication sliding clamp, PCNA, and that this interaction is stimulated by the kinase CDC7. Here we show that another kinase, CDC28, phosphorylates Cac1p on serines 94 and 515 in early S phase and regulates its association with chromatin, but not its association with PCNA. Mutations in the Cac1p-phosphorylation sites of CDC28 but not of CDC7 substantially reduce the in vivo phosphorylation of Cac1p. However, mutations in the putative CDC7 target sites on Cac1p reduce its stability. The association of CAF-I with chromatin is impaired in a cdc28-1 mutant and to a lesser extent in a cdc7-1 mutant. In addition, mutations in the Cac1p-phosphorylation sites by both CDC28 and CDC7 reduce gene silencing at the telomeres. We propose that this phosphorylation represents a regulatory step in the recruitment of CAF-I to chromatin in early S phase that is distinct from the association of CAF-I with PCNA. Hence, we implicate CDC28 in the regulation of chromatin reassembly during DNA replication. These findings provide novel mechanistic insights on the links between cell-cycle regulation, DNA replication and chromatin reassembly.