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首页> 外文期刊>Molecular and Cellular Biology >Transcription Factor UAF, Expansion and Contraction of Ribosomal DNA (rDNA) Repeats, and RNA Polymerase Switch in Transcription of Yeast rDNA
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Transcription Factor UAF, Expansion and Contraction of Ribosomal DNA (rDNA) Repeats, and RNA Polymerase Switch in Transcription of Yeast rDNA

机译：酵母rDNA转录因子UAF，核糖体DNA（rDNA）重复序列的扩增和收缩以及RNA聚合酶转换

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摘要

Strains of the yeast Saccharomyces cerevisiae defective in transcription factor UAF give rise to variants able to grow by transcribing endogenous ribosomal DNA (rDNA) by RNA polymerase II (Pol II). We have demonstrated that the switch to growth using the Pol II system consists of two steps: a mutational alteration in UAF and an expansion of chromosomal rDNA repeats. The first step, a single mutation in UAF, is sufficient to allow Pol II transcription of rDNA. In contrast to UAF mutations, mutations in Pol I or other Pol I transcription factors can not independently lead to Pol II transcription of rDNA, suggesting a specific role of UAF in preventing polymerase switch. The second step, expansion of chromosomal rDNA repeats to levels severalfold higher than the wild type, is required for efficient cell growth. Mutations in genes that affect recombination within the rDNA repeats, fob1 and sir2, decrease and increase, respectively, the frequency of switching to growth using Pol II, indicating that increased rDNA copy number is a cause rather than a consequence of the switch. Finally, we show that the switch to the Pol II system is accompanied by a striking alteration in the localization and morphology of the nucleolus. The altered state that uses Pol II for rDNA transcription is semistable and heritable through mitosis and meiosis. We discuss the significance of these observations in relation to the plasticity of rDNA tandem repeats and nucleolar structures as well as evolution of the Pol I machinery.
机译：转录因子UAF中有缺陷的酵母 Saccharomyces cerevisiae 菌株产生了能够通过RNA聚合酶II（Pol II）转录内源核糖体DNA（rDNA）来生长的变体。我们已经证明，使用Pol II系统向生长的转变包括两个步骤：UAF中的突变改变和染色体rDNA重复序列的扩增。第一步，UAF中的单个突变，足以允许rDNA的Pol II转录。与UAF突变相反，Pol I或其他Pol I转录因子中的突变不能独立导致rDNA的Pol II转录，这表明UAF在防止聚合酶转换中具有特定作用。第二步，有效的细胞生长需要染色体rDNA重复扩增到比野生型高几倍的水平。影响rDNA重复序列内基因重组的基因突变 fob1 和 sir2 分别减少和增加，使用Pol II切换至生长的频率，表明rDNA复制增加数字是切换的原因而不是结果。最后，我们表明切换到Pol II系统伴随着核仁的定位和形态发生显着变化。使用Pol II进行rDNA转录的改变状态是半稳定的，可通过有丝分裂和减数分裂遗传。我们讨论这些观察结果与rDNA串联重复序列和核仁结构的可塑性以及Pol I机制的进化有关的意义。

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