Zaros Cécile, Thuriaux Pierre
Service de Biochimie & Génétique Moléculaire, Bâtiment 144, CEA-Saclay, F-91191, Gif sur Yvette, CEDEX, France.
Mol Microbiol. 2005 Jan;55(1):104-14. doi: 10.1111/j.1365-2958.2004.04375.x.
Rpc25 is a strongly conserved subunit of RNA polymerase III with homology to Rpa43 in RNA polymerase I, Rpb7 in RNA polymerase II and the archaeal RpoE subunit. A central domain of Rpc25 can replaced the corresponding region of Rpb7 with little or no growth defect, underscoring the functional relatedness of these proteins. Rpc25 forms a heterodimer with Rpc17, another conserved component of RNA polymerase III. A conditional mutant (rpc25-S100P) impairs this interaction. rpc25-S100P and another conditional mutant obtained by complementation with the Schizosaccharomyces pombe subunit (rpc25-Sp) were investigated for the properties of their purified RNA polymerase III. The mutant enzymes were defective in the specific synthesis of pre-tRNA transcripts but acted at a wild-type level on poly[d(A-T)] templates. They were also indistinguishable from wild type in transcript elongation, cleavage and termination. These data indicate that Rpc25 is needed for transcription initiation but is not critical for the elongating properties of RNA polymerase III.
Rpc25是RNA聚合酶III的一个高度保守亚基，与RNA聚合酶I中的Rpa43、RNA聚合酶II中的Rpb7以及古细菌RpoE亚基具有同源性。Rpc25的一个中央结构域可以替代Rpb7的相应区域，且几乎没有生长缺陷，这突出了这些蛋白质的功能相关性。Rpc25与Rpc17形成异二聚体，Rpc17是RNA聚合酶III的另一个保守组分。一个条件性突变体（rpc25-S100P）损害了这种相互作用。研究了rpc25-S100P以及通过与粟酒裂殖酵母亚基互补获得的另一个条件性突变体（rpc25-Sp）纯化后的RNA聚合酶III的特性。突变酶在前体tRNA转录本的特异性合成方面存在缺陷，但在聚[d(A-T)]模板上的活性与野生型水平相当。它们在转录延伸、切割和终止方面也与野生型没有区别。这些数据表明，Rpc25是转录起始所必需的，但对RNA聚合酶III的延伸特性并不关键。
