Dohke Kohei, Miyazaki Shota, Tanaka Katsunori, Urano Takeshi, Grewal Shiv I S, Murakami Yota
Department of Cell Biology, Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507 Japan.
Genes Cells. 2008 Oct;13(10):1027-43. doi: 10.1111/j.1365-2443.2008.01225.x. Epub 2008 Aug 29.
Chromatin assembly factor-1 (CAF1) is a well-conserved histone chaperone that loads the histone H3-H4 complex onto newly synthesized DNA in vitro through interaction with the replication factor PCNA. CAF1 is considered to be involved in heterochromatin maintenance in several organisms, but the evidence is circumstantial and functional details have not been established. We identified fission yeast CAF-1 (spCAF1), which interacts with PCNA in S phase. Depletion of spCAF1 caused defects in silencing at centromeric and mating locus heterochromatin, accompanied with a decrease in Swi6, the fission yeast HP1 homologue. Loss of spCAF1 destabilized both the silent and active states of chromatin at the meta-stable heterochromatic region, with a more pronounced effect on the silent state, indicating that spCAF1 is involved in the maintenance of heterochromatin. Swi6 dissociated from heterochromatin during G1/S phase appears to associate with spCAF1. In early S phase, spCAF1 localized to replicating heterochromatin as well as euchromatin and remained associated with Swi6, and Swi6 then bound to heterochromatin. Taken together, we propose that spCAF1 functions in heterochromatin maintenance by recruiting dislocated Swi6 during replication to replicated heterochromatin at the replication fork.
染色质组装因子-1（CAF1）是一种高度保守的组蛋白伴侣，它在体外通过与复制因子PCNA相互作用，将组蛋白H3-H4复合物加载到新合成的DNA上。CAF1被认为在多种生物体中参与异染色质的维持，但证据是间接的，功能细节尚未明确。我们鉴定出了裂殖酵母CAF-1（spCAF1），它在S期与PCNA相互作用。spCAF1的缺失导致着丝粒和交配位点异染色质沉默出现缺陷，同时裂殖酵母HP1同源物Swi6减少。spCAF1的缺失使亚稳定异染色质区域染色质的沉默和活跃状态均不稳定，对沉默状态的影响更为明显，表明spCAF1参与异染色质的维持。在G1/S期从异染色质解离的Swi6似乎与spCAF1结合。在S期早期，spCAF1定位于正在复制的异染色质以及常染色质，并与Swi6保持结合，然后Swi6结合到异染色质上。综上所述，我们提出spCAF1通过在复制过程中将错位的Swi6招募到复制叉处已复制的异染色质上，从而在异染色质维持中发挥作用。
