Bier Mirko, Fath Stephan, Tschochner Herbert
Biochemie-Zentrum Heidelberg, Im Neuenheimer Feld 328, D-69120 Heidelberg, Germany.
FEBS Lett. 2004 Apr 23;564(1-2):41-6. doi: 10.1016/S0014-5793(04)00311-4.
The amounts of RNA polymerase I (Pol I) and basal rDNA transcription factors were determined in yeast whole cell extracts. A 17-fold excess of Pol I was found compared to the Pol I-specific initiation factors upstream activating factor (UAF) and core factor (CF) which underlines that both initiation factors interact with a minor fraction of Pol I when rDNA transcription is active. Surprisingly, Rrn3p, another Pol I-specific initiation factor, is more abundant in cell lysates than UAF and CF. Our analyses revealed that a large fraction of cellular Rrn3p is not associated with Pol I. However, the amount of initiation-active Rrn3p which forms a stable complex with Pol I corresponds to the levels of UAF and CF which have been shown to bind the promoter. Initiation-active Rrn3p dissociates from the template during or immediately after Pol I has switched from initiation to elongation. Our data support a model in which the elongating Pol I leaves the initiation factors UAF, CF and Rrn3p close by the promoter.
在酵母全细胞提取物中测定了RNA聚合酶I（Pol I）和基础核糖体DNA转录因子的含量。结果发现，与Pol I特异性起始因子上游激活因子（UAF）和核心因子（CF）相比，Pol I过量17倍，这表明当核糖体DNA转录活跃时，这两种起始因子仅与一小部分Pol I相互作用。令人惊讶的是，另一种Pol I特异性起始因子Rrn3p在细胞裂解物中的含量比UAF和CF更高。我们的分析表明，细胞内大部分Rrn3p并不与Pol I结合。然而，与Pol I形成稳定复合物的起始活性Rrn3p的量与已证明能结合启动子的UAF和CF的水平相当。在Pol I从起始转变为延伸过程中或之后，起始活性Rrn3p会从模板上解离。我们的数据支持这样一种模型，即延伸中的Pol I使起始因子UAF、CF和Rrn3p留在启动子附近。
