Koch C, Wollmann P, Dahl M, Lottspeich F
Institut für Genetik der Universität München, Maria-Ward-Strasse 1a, D-80638 München, Germany.
Nucleic Acids Res. 1999 May 15;27(10):2126-34. doi: 10.1093/nar/27.10.2126.
Entry into the cell cycle in budding yeast involves transcriptional activation of G1cyclin genes and DNA synthesis genes when cells reach a critical size in late G1. Expression of G1cyclins CLN1 and CLN2 is regulated by the transcription factor SBF (composed of Swi4p and Swi6p) and depends on the cyclin-dependent Cdc28 protein kinase and cyclin Cln3p. To identify novel regulators of SBF-dependent gene expression we screened for mutants that fail to activate transcription of G1cyclins. We found mutations in a gene called CTR9. ctr9 mutants are inviable at 37 degrees C and accumulate large cells. CTR9 is identical to CDP1. CTR9 encodes a conserved nuclear protein of 125 kDa containing several TPR repeats implicated in protein-protein interactions. We show that Ctr9p is a component of a high molecular weight protein complex. Using immuno-affinity chromatography we found that Ctr9p associates with polypeptides of 50 and 65 kDa. By mass spectrometry these were identified as Cdc73p and Paf1p. We show that Paf1p, like Ctr9p, is required for efficient CLN2 transcription, whereas Cdc73p is not. Paf1p and Cdc73p were previously reported to be RNA poly-merase II-associated proteins, suggesting that the Ctr9p complex may interact with the general transcription apparatus.
芽殖酵母进入细胞周期涉及到当细胞在G1晚期达到临界大小时G1周期蛋白基因和DNA合成基因的转录激活。G1周期蛋白CLN1和CLN2的表达受转录因子SBF（由Swi4p和Swi6p组成）调控，并依赖于细胞周期蛋白依赖性Cdc28蛋白激酶和细胞周期蛋白Cln3p。为了鉴定SBF依赖性基因表达的新调节因子，我们筛选了不能激活G1周期蛋白转录的突变体。我们在一个名为CTR9的基因中发现了突变。ctr9突变体在37℃时无法存活，并积累大细胞。CTR9与CDP1相同。CTR9编码一种125 kDa的保守核蛋白，含有几个与蛋白质-蛋白质相互作用有关的TPR重复序列。我们表明Ctr9p是一种高分子量蛋白质复合物的组成部分。使用免疫亲和层析，我们发现Ctr9p与50 kDa和65 kDa的多肽结合。通过质谱分析，这些多肽被鉴定为Cdc73p和Paf1p。我们表明，与Ctr9p一样，Paf1p是高效转录CLN2所必需的，而Cdc73p则不是。Paf1p和Cdc73p先前被报道为与RNA聚合酶II相关的蛋白质，这表明Ctr9p复合物可能与通用转录装置相互作用。
