芽殖酵母和裂殖酵母中异染色质形成机制

Heterochromatin Formation in Saccharomyces cerevisiae and Schizosaccharomyces pombe

芽殖酵母(Saccharomyces cerevisiae)和裂殖酵母(Schizosaccharomyces pombe)是用来研究异染色质形成、细胞周期、DNA复制等重要细胞功能的理想单细胞真核生物.本文主要介绍这2种酵母中异染色质形成的机制.异染色质是一种抑制基因转录和DNA重组的特殊染色质结构.尽管在芽殖酵母和裂殖酵母中异染色质形成都需要组蛋白修饰,但异染色质建立的机制不同.在芽殖酵母中参与异染色质形成的主要蛋白是Sir1-4蛋白(其中Sir2为组蛋白H3去乙酰化酶),而组蛋白H3赖氨酸9甲基化酶Clr4和异染色质蛋白Swi6在裂殖酵母异染色质形成中起关键的作用.在这两个酵母中,参与异染色质形成的组蛋白修饰蛋白由DNA结合蛋白招募到异染色质.此外,裂殖酵母也利用RNA干扰系统招募组蛋白修饰蛋白.

The budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe are two ideal eukaryotic model organisms for the study of important cellular functions including heterochromatin formation, cell cycle and DNA replication. In this article, we reviewed heterochromatin formation in these two distantly related yeasts. Heterochromatin is a specialized chromatin structure that inhibits transcription and DNA recombination. Although heterochromatin formation in these two yeasts involves self-perpetuating modifications of histones, the yeasts use different mechanisms to establish heterochromatin. Heterochromatin formation in S. cerevisiae is mediated by Sir proteins including histone H3 deacetylase Sir2. In contrast, histone H3-1ysine 9 methyhransferase Clr4 and heterochromatin protein Swi6 play a key role in heterochromatin formation in S. pombe. While the histone modifying enzymes involved in heterochromatin formation in these two yeasts are recruited by DNA-binding proteins, in fission yeast, they are also recruited by the RNA interference （RNAi） machinery.