Hayashi Makoto T, Takahashi Tatsuro S, Nakagawa Takuro, Nakayama Jun-ichi, Masukata Hisao
Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka, 560-0043 Japan.
Nat Cell Biol. 2009 Mar;11(3):357-62. doi: 10.1038/ncb1845. Epub 2009 Feb 1.
Heterochromatin is a structurally compacted region of chromosomes in which transcription and recombination are inactivated. DNA replication is temporally regulated in heterochromatin, but the molecular mechanism for regulation has not been elucidated. Among heterochromatin loci in Schizosaccharomyces pombe, the pericentromeric region and the silent mating-type (mat) locus replicate in early S phase, whereas the sub-telomeric region does not, suggesting complex mechanisms for regulation of replication in heterochromatic regions. Here, we show that Swi6, an S. pombe counterpart of heterochromatin protein 1 (HP1), is required for early replication of the pericentromeric region and the mat locus. Origin-loading of Sld3, which depends on Dfp1/Dbf4-dependent kinase Cdc7 (DDK), is stimulated by Swi6. An HP1-binding motif within Dfp1 is required for interaction with Swi6 in vitro and for early replication of the pericentromeric region and mat locus. Tethering of Dfp1 to the pericentromeric region and mat locus in swi6-deficient cells restores early replication of these loci. Our results show that a heterochromatic protein positively regulates initiation of replication in silenced chromatin by interacting with an essential kinase.
异染色质是染色体的结构紧密区域，其中转录和重组处于失活状态。异染色质中的DNA复制受到时间调控，但其调控的分子机制尚未阐明。在粟酒裂殖酵母的异染色质位点中，着丝粒周围区域和沉默交配型（mat）位点在S期早期复制，而亚端粒区域则不然，这表明异染色质区域的复制调控机制复杂。在这里，我们表明，异染色质蛋白1（HP1）在粟酒裂殖酵母中的对应物Swi6，是着丝粒周围区域和mat位点早期复制所必需的。依赖于Dfp1/Dbf4依赖性激酶Cdc7（DDK）的Sld3起始装载，受到Swi6的刺激。Dfp1内的一个HP1结合基序对于体外与Swi6相互作用以及着丝粒周围区域和mat位点的早期复制是必需的。在swi6缺陷细胞中将Dfp1拴系到着丝粒周围区域和mat位点可恢复这些位点的早期复制。我们的结果表明，一种异染色质蛋白通过与一种必需激酶相互作用，正向调节沉默染色质中的复制起始。
