The Saccharomyces cerevisiae Sub2 protein suppresses heterochromatic silencing at telomeres and subtelomeric genes
The Saccharomyces cerevisiae Sub2 protein suppresses heterochromatic silencing at telomeres and subtelomeric genes
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作者：
Lahue, E;Heckathorn, J;Wolfe, C
我们发现，Sub2p，一个多功能的酿酒酵母解旋酶家族成员，参与mRNA的延伸和运输，过表达也抑制异染色质沉默在端粒。遗传分析显示，当选择端粒沉默的URA3报告基因时，从高拷贝质粒过表达SUB2的细胞表现出增加的存活率。两个温度敏感的sub2突变，影响不同的解旋酶结构域也在允许的温度下进行了检查，这些突变体也克服了URA3报告沉默。沉默被抑制的程度与SUB2 RNA和蛋白水平相关。此外，我们发现，Sub2p定位于端粒，染色质免疫沉淀测定，这表明Sub2p在端粒有直接的影响。转录本的全基因组分析用于评估Sub2p过度产生是否仅影响沉默的URA3报告基因，或者是否其他亚端粒基因也受到影响。在Sub2p过表达细胞中升高的70种RNA转录物中，28%由位于核心X或Y'重复序列的5Kbp内的亚端粒基因编码。其余的转录本聚集成几个功能组，包括铁稳态途径，嘌呤核苷酸代谢和杂项运输基因等。这些结果表明Sub2p对转录的靶向作用。我们的研究结果也证实，Sub2p影响异染色质基因的表达，类似于观察到的果蝇Hel25E同源。上述观察结果表明，Sub2p除了影响染色质结构之外，还影响或平行于其在转录延伸、剪接和mRNA转运中的功能。版权所有（c）2005年约翰威利父子有限公司。
We show that overexpression of Sub2p, a multifunctional Saccharomyces cerevisiae helicase family member that is involved in mRNA elongation and transport, also suppresses heterochromatic silencing at telomeres. Genetic assays show cells that overexpress SUB2 from a high copy plasmid exhibit increased survival rates when selecting for a telomere-silenced URA3 reporter. Two temperature-sensitive sub2 mutations that affect different helicase domains were also examined at the permissive temperature; these mutants also overcome silencing of the URA3 reporter. The degree to which silencing is suppressed correlates with SUB2 RNA and protein levels. Additionally, we find that Sub2p localizes to the telomeres, as determined by chromatin immunoprecipitation assays, suggesting that Sub2p has a direct effect at telomeres. Genome-wide analysis of transcripts was used to assess whether Sub2p overproduction affects only the silenced URA3 reporter gene, or whether other subtelomeric genes are also affected. Of the 70 RNA transcripts elevated in the Sub2p overexpressing cells, 28% are encoded by subtelomeric genes that are located within 5 Kbp of a core X or Y' repeat. The remainder of the transcripts clustered into several functional groups, including the iron homeostasis pathway, purine nucleotide metabolism, and miscellaneous transport genes, among others. These results suggest a targeted effect of Sub2p on transcription. Our results also confirm that Sub2p affects heterochromatic gene expression, similar to that observed with the Drosophila Hel25E homologue. The above observations imply that Sub2p affects chromatin structure in addition to, or in parallel with, its functions in transcription elongation, splicing and mRNA transport. Copyright (c) 2005 John Wiley & Sons, Ltd.