Two distinct pathways responsible for the loading of CENP-A to centromeres in the fission yeast cell cycle
Two distinct pathways responsible for the loading of CENP-A to centromeres in the fission yeast cell cycle
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DOI：
10.1098/rstb.2004.1614
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发表时间：
2005-03-29
影响因子：
6.3
通讯作者：
Saitoh, S
中科院分区：
文献类型：
--
作者：
Takahashi, K;Takayama, Y;Saitoh, S
CENP-A是一种着丝粒特异性组蛋白H3变体，其对于迄今为止研究的所有真核生物中的忠实染色体分离是必不可少的。我们从遗传学上鉴定了两个因子，Ams 2和Mis 6，每个因子都是正确定位SpCENP-A（Cnp 1）（CENP-A的裂变酵母同源物）的着丝粒所需的。Ams 2是细胞周期调节的加塔因子，在S期定位于核染色质上，包括着丝粒上。Ams 2可能是负责复制耦合加载SpCENP-A通过促进核小体形成在S期。一致的是，组蛋白H4的过量产生，而不是H3的过量产生，抑制了Ams 2缺陷细胞中SpCENP-A定位的缺陷。我们证明了在细胞周期中存在至少两个不同的SpCENP-A加载阶段：S期和晚期G2期。异位诱导的SpCENP-A被有效地加载到G2期阻滞细胞的着丝粒上，表明SpCENP-A可能在S期完成后经历复制解偶联加载。SpCENP-A的G2加载途径可能需要Mis 6，Mis 6是一种组成型着丝粒结合蛋白，也参与Mad 2依赖性纺锤体附着检查点反应。在这里，我们讨论了CENP-A的灵活加载机制和裂殖酵母中着丝粒染色质形成的可塑性之间的功能关系。
CENP-A is a centromere-specific histone H3 variant that is- essential for faithful chromosome segregation in all eukaryotes thus far investigated. We genetically identified two factors, Ams2 and Mis6, each of which is required for the correct centromere localization of SpCENP-A (Cnp1), the fission yeast homologue of CENP-A. Ams2 is a cell-cycle-regulated GATA factor that localizes on the nuclear chromatin, including on centromeres, during the S phase. Ams2 may be responsible for the replication-coupled loading of SpCENP-A by facilitating nucleosomal formation during the S phase. Consistently, overproduction of histone H4, but not that of H3, suppressed the defect of SpCENP-A localization in Ams2-deficient cells. We demonstrated the existence of at least two distinct phases for SpCENP-A loading during the cell cycle: the S phase and the late-G2 phase. Ectopically induced SpCENP-A was efficiently loaded onto the centromeres in G2-arrested cells, indicating that SpCENP-A probably undergoes replication-uncoupled loading after the completion of S phase. This G2 loading pathway of SpCENP-A may require Mis6, a constitutive centromere-binding protein that is also implicated in the Mad2-dependent spindle attachment checkpoint response. Here, we discuss the functional relationship between the flexible loading mechanism of CENP-A and the plasticity of centromere chromatin formation in fission yeast.