Henikoff S, Ahmad K, Platero J S, van Steensel B
Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109-1024, USA.
Proc Natl Acad Sci U S A. 2000 Jan 18;97(2):716-21. doi: 10.1073/pnas.97.2.716.
Centromeres of most organisms are embedded within constitutive heterochromatin, the condensed regions of chromosomes that account for a large fraction of complex genomes. The functional significance of this centromere-heterochromatin relationship, if any, is unknown. One possibility is that heterochromatin provides a suitable environment for assembly of centromere components, such as special centromeric nucleosomes that contain distinctive histone H3-like proteins. We describe a Drosophila H3-like protein, Cid (for centromere identifier) that localizes exclusively to fly centromeres. When the cid upstream region drives expression of H3 and H2B histone-green fluorescent protein fusion genes in Drosophila cells, euchromatin-specific deposition results. Remarkably, when the cid upstream region drives expression of yeast, worm, and human centromeric histone-green fluorescent protein fusion proteins, localization is preferentially within Drosophila pericentric heterochromatin. Heterochromatin-specific localization also was seen for yeast and worm centromeric proteins constitutively expressed in human cells. Preferential localization to heterochromatin in heterologous systems is unexpected if centromere-specific or site-specific factors determine H3-like protein localization to centromeres. Rather, the heterochromatic state itself may help localize centromeric components.
大多数生物体的着丝粒都嵌入在组成型异染色质中，组成型异染色质是染色体的浓缩区域，在复杂基因组中占很大比例。这种着丝粒与异染色质关系的功能意义（如果有的话）尚不清楚。一种可能性是，异染色质为着丝粒组件的组装提供了合适的环境，例如包含独特组蛋白H3样蛋白的特殊着丝粒核小体。我们描述了一种果蝇H3样蛋白，Cid（着丝粒标识符），它专门定位于果蝇着丝粒。当cid上游区域驱动果蝇细胞中H3和H2B组蛋白-绿色荧光蛋白融合基因的表达时，会导致常染色质特异性沉积。值得注意的是，当cid上游区域驱动酵母、线虫和人类着丝粒组蛋白-绿色荧光蛋白融合蛋白的表达时，定位优先在果蝇着丝粒周围的异染色质内。在人类细胞中组成型表达的酵母和线虫着丝粒蛋白也观察到异染色质特异性定位。如果着丝粒特异性或位点特异性因子决定H3样蛋白着丝粒定位，那么在异源系统中优先定位于异染色质是出乎意料的。相反，异染色质状态本身可能有助于着丝粒组件的定位。
