Yeast RNA polymerase I enhancer is dispensable for transcription of the chromosomal rRNA gene and cell growth, and its apparent transcription enhancement from ectopic promoters requires Fob1 protein
Yeast RNA polymerase I enhancer is dispensable for transcription of the chromosomal rRNA gene and cell growth, and its apparent transcription enhancement from ectopic promoters requires Fob1 protein
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DOI：
10.1128/mcb.21.16.5541-5553.2001
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发表时间：
2001-08-01
影响因子：
5.3
通讯作者：
Nomura, M
中科院分区：
文献类型：
--
作者：
Wai, H;Johzuka, K;Nomura, M
酿酒酵母核糖体 DNA (rDNA) 重复序列中 35S rRNA 基因的末端有一个增强子，该增强子已被证明可以极大地刺激异位报告系统中的 rDNA 转录。然而，我们发现增强子对于从染色体 rDNA 合成正常水平的 rRNA 或细胞生长来说并不是必需的。删除了整个 rDNA 增强子的酵母菌株在生长或 rRNA 合成方面没有表现出任何缺陷。我们发现，在核仁结构破坏的细胞中没有观察到增强子对异位报告基因的刺激活性，这表明报告基因通常很难接近核仁中的 RNA 聚合酶 I (Pol I) 机器，而增强子提高了可接近性。我们还发现，fob1 突变消除了集成在 HIS4 基因座上的增强子依赖性 rDNA 启动子的转录，而对染色体 rDNA 的转录没有任何影响。 FOB1 是重组热点 (HOT1) 活性（也需要增强子区域）和 rDNA 重复序列内重组所必需的。我们认为 Fob1 蛋白通过增强子区域刺激 rDNA 重复序列之间的相互作用，从而帮助异位 rDNA 启动子招募通常存在于核仁中的 Pol I 机制。
At the end of the 35S rRNA gene within ribosomal DNA (rDNA) repeats in Saccharomyces cerevisiae lies an enhancer that has been shown to greatly stimulate rDNA transcription in ectopic reporter systems. We found, however, that the enhancer is not necessary for normal levels of rRNA synthesis from chromosomal rDNA or for cell growth. Yeast strains which have the entire enhancer from rDNA deleted did not show any defects in growth or rRNA synthesis. We found that the stimulatory activity of the enhancer for ectopic reporters is not observed in cells with disrupted nucleolar structures, suggesting that reporter genes are in general poorly accessible to RNA polymerase I (Pol I) machinery in the nucleolus and that the enhancer improves accessibility. We also found that a fob1 mutation abolishes transcription from the enhancer-dependent rDNA promoter integrated at the HIS4 locus without any effect on transcription from chromosomal rDNA. FOB1 is required for recombination hot spot (HOT1) activity, which also requires the enhancer region, and for recombination within rDNA repeats. We suggest that Fob1 protein stimulates interactions between rDNA repeats through the enhancer region, thus helping ectopic rDNA promoters to recruit the Pol I machinery normally present in the nucleolus.