TPR proteins as essential components of the yeast cell cycle.
TPR proteins as essential components of the yeast cell cycle.
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DOI：
10.1101/sqb.1991.056.01.075
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发表时间：
1991
期刊：
影响因子：
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通讯作者：
R. Sikorski;W. Michaud;J. Wootton;M. Boguski;C. Connelly;P. Hieter
中科院分区：
文献类型：
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作者：
R. Sikorski;W. Michaud;J. Wootton;M. Boguski;C. Connelly;P. Hieter
染色体分离是真核生物的基本过程，可确保遗传物质在每个细胞分裂周期中忠实分布。对酵母、青蛙、海胆和人类等多种生物体进行的实验表明，染色体传递所需的基本结构和功能在整个进化过程中得到了保留。酵母研究利用遗传技术来揭示对于分离过程至关重要或对其高保真度有重要贡献的基因（Nurse 1985；有关综述，请参见 Spencer 等人 1990）。有丝分裂必需成分的候选者可能存在于酵母细胞分裂周期 (cdc) 突变体中，它们在 DNA 合成后但有丝分裂纺锤体伸长之前阻断细胞周期进程 (Pringle 和 Hartwell 1981)。 Cdc28 蛋白激酶在调节进入有丝分裂中发挥 pivitol 作用，似乎是 G2/M 组的成员（Piggott 等人，1982 年；Ghiara 等人，1991 年；Surana 等人，1991 年）。此外，其他 cdc 突变体的子集在酿酒酵母中产生类似的 G2/M 突变体表型，包括 cdc9、cdcl3、cdc16、cdc17、cdc20 和 cdc23。在不允许的温度下，这些突变体在 DNA 合成完成后和纺锤体伸长前以大芽细胞的形式停滞，芽颈中具有未分裂的细胞核。由于染色体丢失，任何这些基因的亚形性突变都会导致非整倍性水平升高（Hartwell 和 Smith 1985），但 CDC9、CDC13 和 CDC17 的突变也会导致有丝分裂重组水平升高。后一种表型表明参与 DNA 修复途径 (Resnick 1979)，事实上，CDC17 和 CDC9 已被证明分别编码 DNA 聚合酶 (Carson 1987) 和 DNA 连接酶 (Johnston 和 Nasmyth 1978)。此外，cdc9、cdc13 和 cdc17 突变体中触发的统一 G 2 末端阻滞形态依赖于 RAD9 基因，该基因的产物被认为可以监测基因组内 DNA 的结构完整性（Weinert 和 Hartwell 1988；Brown 等人，本卷）。相比之下，cdc16、cdc20和cdc23在有丝分裂重组方面表现出很少或没有增加，并且其G 2 末端阻滞形态不依赖于RAD9基因产物。根据这些标准，CDC16、CDC20 和 CDC23 似乎更直接地参与有丝分裂早期阶段的染色体分离机制。为了启动 CDC23 的分子研究，我们克隆了该基因并检查了预测的 CDC23 多肽的结构（Sikorski 等人，1990）。我们的结果表明，CDC23 与 CDC16 以及其他蛋白质家族相关，所有这些蛋白质都包含 34 个残基的新型重复氨基酸基序（TPR 基序）。这些重复序列的功能尚不清楚，但据推测它们可能形成两亲性 c-螺旋，原则上可以指导蛋白质-蛋白质相互作用（Hirano 等人，1990；Sikorski 等人，1990）。最近描述了更广泛的 TPR 蛋白功能假设模型（Goebl 和 Yanagida 1991）。我们继续对 CDC23 进行研究，重点是 TPR 单元在执行生物功能中的作用。我们在这里回顾我们在这个 TPR 基因以及另一个 TPR 家族成员 SNB1 的发现和分析方面的进展。我们还更新了当前的 TPR 家族成员列表，其中包括第一个细菌示例，并对各个家族成员之间的序列关系进行了定量分析。
Chromosome segregation is a fundamental eukaryotic process that ensures faithful distribution of genetic material during each cell division cycle. Experiments in a variety of organisms including yeast, frogs, sea urchins, and humans have shown that the basic structures and functions required for chromosome transmission have been conserved throughout evolution. Studies in yeast have exploited genetic techniques to uncover genes that are essential for the segregation process or important for contributing to its high fidelity (Nurse 1985; for review, see Spencer et al. 1990). Candidates for essential mitotic components may be found in the group of yeast cell division cycle (cdc) mutants that block cell cycle progression after DNA synthesis but prior to elongation of the mitotic spindle (Pringle and Hartwell 1981). The Cdc28 protein kinase, which plays a pivitol role in regulating the entry into mitosis, appears to be a member of this G2/M group (Piggott et al. 1982; Ghiara et al. 1991; Surana et al. 1991). In addition, a subset of other cdc mutants yield similar G2/M mutant phenotypes in Saccharomyces cerevisiae, including cdc9, cdcl3, cdc16, cdc17, cdc20, and cdc23. At their nonpermissive temperatures, these mutants arrest after the completion of DNA synthesis and before spindle elongation in the form of large budded cells with an undivided nucleus in the neck of the bud. Hypomorphic mutations in any of these genes produce increased levels of aneuploidy due to chromosome loss (Hartwell and Smith 1985), but mutations in CDC9, CDC13, and CDC17 also result in elevated levels of mitotic recombination. This latter phenotype suggests participation in a DNA-repair pathway (Resnick 1979), and indeed, CDC17 and CDC9 have been shown to encode a DNA polymerase (Carson 1987) and DNA ligase (Johnston and Nasmyth 1978), respectively. Furthermore, the uniform G 2 terminal arrest morphology triggered in cdc9, cdc13, and cdc17 mutants is dependent on the RAD9 gene, whose product is thought to monitor the structural integrity of DNA within the genome (Weinert and Hartwell 1988; Brown et al., this volume). In contrast, cdc16, cdc20, and cdc23 exhibit little or no increase in mitotic recombination and are not dependent on the RAD9 gene product for their G 2 terminal arrest morphology. By these criteria, CDC16, CDC20, and CDC23 seem to be more directly involved in the mechanisms of chromosome segregation during an early stage of mitosis. To initiate molecular studies of CDC23, we cloned the gene and examined the structure of the predicted CDC23 polypeptide (Sikorski et al. 1990). Our results showed that CDC23 is related to CDC16 as well as a family of other proteins, all of which contain versions of a novel, repeating amino acid motif of 34 residues (TPR motif). The function of these repeats is not known, but it has been postulated that they may form amphipathic c~-helices that could in principle direct protein-protein interactions (Hirano et al. 1990; Sikorski et al. 1990). More extensive hypothetical models of TPR protein function have been described recently (Goebl and Yanagida 1991). We have continued our studies of CDC23 with an emphasis on the role of the TPR units in executing biological function. We review here our progress on this TPR gene and on the discovery and analysis of an additional TPR family member, SNB1. We have also updated the current list of TPR family members, which includes the first bacterial example, and present quantitative analysis of the sequence relationships among the various family members.