Fourel G, Revardel E, Koering C E, Gilson E
Laboratoire de Biologie Moléculaire et Cellulaire, Ecole Normale Supérieure de Lyon, UMR5665 CNRS/ENSL, 69364 Lyon Cedex 07, France.
EMBO J. 1999 May 4;18(9):2522-37. doi: 10.1093/emboj/18.9.2522.
In budding yeast, the telomeric DNA is flanked by a combination of two subtelomeric repetitive sequences, the X and Y' elements. We have investigated the influence of these sequences on telomeric silencing. The telomere-proximal portion of either X or Y' dampened silencing when located between the telomere and the reporter gene. These elements were named STARs, for subtelomeric anti-silencing regions. STARs can also counteract silencer-driven repression at the mating-type HML locus. When two STARs bracket a reporter gene, its expression is no longer influenced by surrounding silencing elements, although these are still active on a second reporter gene. In addition, an intervening STAR uncouples the silencing of neighboring genes. STARs thus display the hallmarks of insulators. Protection from silencing is recapitulated by multimerized oligonucleotides representing Tbf1p- and Reb1p-binding sites, as found in STARs. In contrast, sequences located more centromere proximal in X and Y' elements reinforce silencing. They can promote silencing downstream of an insulated expressed domain. Overall, our results suggest that the silencing emanating from telomeres can be propagated in a discontinuous manner via a series of subtelomeric relay elements.
在出芽酵母中，端粒DNA两侧是两个亚端粒重复序列X和Y’元件的组合。我们研究了这些序列对端粒沉默的影响。当位于端粒和报告基因之间时，X或Y’的端粒近端部分会减弱沉默作用。这些元件被命名为STARs，即亚端粒抗沉默区域。STARs还可以对抗沉默子驱动的在交配型HML位点的抑制作用。当两个STARs将一个报告基因包围时，其表达不再受周围沉默元件的影响，尽管这些沉默元件对另一个报告基因仍有活性。此外，一个插入的STAR会解除相邻基因的沉默作用。因此，STARs表现出绝缘子的特征。STARs中发现的代表Tbf1p和Reb1p结合位点的多聚化寡核苷酸可重现对沉默的保护作用。相比之下，X和Y’元件中更靠近着丝粒的序列会增强沉默作用。它们可以促进绝缘表达结构域下游的沉默作用。总体而言，我们的结果表明，端粒产生的沉默作用可以通过一系列亚端粒中继元件以不连续的方式传播。
