Collins Nadine, Poot Raymond A, Kukimoto Iwao, García-Jiménez Custodia, Dellaire Graham, Varga-Weisz Patrick D
Marie Curie Research Institute, The Chart, Oxted, Surrey RH8 0TL, UK.
Nat Genet. 2002 Dec;32(4):627-32. doi: 10.1038/ng1046. Epub 2002 Nov 18.
The mechanism by which the eukaryotic DNA-replication machinery penetrates condensed chromatin structures to replicate the underlying DNA is poorly understood. Here we provide evidence that an ACF1-ISWI chromatin-remodeling complex is required for replication through heterochromatin in mammalian cells. ACF1 (ATP-utilizing chromatin assembly and remodeling factor 1) and an ISWI isoform, SNF2H (sucrose nonfermenting-2 homolog), become specifically enriched in replicating pericentromeric heterochromatin. RNAi-mediated depletion of ACF1 specifically impairs the replication of pericentromeric heterochromatin. Accordingly, depletion of ACF1 causes a delay in cell-cycle progression through the late stages of S phase. In vivo depletion of SNF2H slows the progression of DNA replication throughout S phase, indicating a functional overlap with ACF1. Decondensing the heterochromatin with 5-aza-2-deoxycytidine reverses the effects of ACF1 and SNF2H depletion. Expression of an ACF1 mutant that cannot interact with SNF2H also interferes with replication of condensed chromatin. Our data suggest that an ACF1-SNF2H complex is part of a dedicated mechanism that enables DNA replication through highly condensed regions of chromatin.
真核生物DNA复制机制如何穿透浓缩的染色质结构以复制其下的DNA，目前了解甚少。在此我们提供证据表明，ACF1-ISWI染色质重塑复合体是哺乳动物细胞中通过异染色质进行复制所必需的。ACF1（利用ATP的染色质组装和重塑因子1）和一种ISWI亚型SNF2H（蔗糖非发酵-2同源物）在复制中的着丝粒周围异染色质中特异性富集。RNA干扰介导的ACF1缺失特异性损害着丝粒周围异染色质的复制。因此，ACF1的缺失导致细胞周期在S期后期的进程延迟。体内SNF2H的缺失减缓了整个S期DNA复制的进程，表明其与ACF1存在功能重叠。用5-氮杂-2'-脱氧胞苷使异染色质解聚可逆转ACF1和SNF2H缺失的影响。不能与SNF2H相互作用的ACF1突变体的表达也会干扰浓缩染色质的复制。我们的数据表明，ACF1-SNF2H复合体是一种专门机制的一部分，该机制使DNA能够通过高度浓缩的染色质区域进行复制。
