Delattre M, Spierer A, Tonka C H, Spierer P
Department of Zoology and Animal Biology, University of Geneva, CH-1211 Geneva 4, Switzerland.
J Cell Sci. 2000 Dec;113 Pt 23:4253-61. doi: 10.1242/jcs.113.23.4253.
Position-effect variegation results from mosaic silencing by chromosomal rearrangements juxtaposing euchromatin genes next to pericentric heterochromatin. An increase in the amounts of the heterochromatin-associated Su(var)3-7 and HP1 proteins augments silencing. Using the yeast two-hybrid protein interaction trap system, we have isolated HP1 using Su(var)3-7 as a bait. We have then delimited three binding sites on Su(var)3-7 for HP1. On HP1, the C-terminal moiety, including the chromo shadow domain, is required for interaction. In vivo, both proteins co-localise not only in heterochromatin, but also in a limited set of sites in euchromatin and at telomeres. When delocalised to the sites bound by the protein Polycomb in euchromatin, HP1 recruits Su(var)3-7. Finally, and in contrast with euchromatin genes, a decrease in the amounts of both proteins enhances variegation of the light gene, one of the few genetic loci mapped within pericentric heterochromatin. This body of data supports a direct link between Su(var)3-7 and HP1 in the genomic silencing of position-effect variegation.
位置效应斑驳是由染色体重排导致的镶嵌沉默引起的，染色体重排使常染色质基因与着丝粒周围异染色质相邻。异染色质相关的Su(var)3-7和HP1蛋白数量的增加会增强沉默作用。利用酵母双杂交蛋白相互作用捕获系统，我们以Su(var)3-7作为诱饵分离出了HP1。然后我们在Su(var)3-7上划定了三个与HP1的结合位点。在HP1上，包括染色体阴影结构域在内的C末端部分是相互作用所必需的。在体内，这两种蛋白不仅在异染色质中共定位，而且在常染色质的一组有限位点以及端粒处也共定位。当HP1异位定位于常染色质中与多梳蛋白结合的位点时，它会招募Su(var)3-7。最后，与常染色质基因相反，这两种蛋白数量的减少会增强亮基因的斑驳现象，亮基因是少数定位于着丝粒周围异染色质内的基因位点之一。这一系列数据支持了Su(var)3-7和HP1在位置效应斑驳的基因组沉默中存在直接联系。
