al-Khodairy F, Fotou E, Sheldrick K S, Griffiths D J, Lehmann A R, Carr A M
MRC Cell Mutation Unit, Sussex University, Falmer, United Kingdom.
Mol Biol Cell. 1994 Feb;5(2):147-60. doi: 10.1091/mbc.5.2.147.
To investigate the mechanisms that ensure the dependency relationships between cell cycle events and to investigate the checkpoints that prevent progression through the cell cycle after DNA damage, we have isolated mutants defective in the checkpoint and feedback control pathways. We report the isolation and characterization of 11 new loci that define distinct classes of mutants defective in one or more of the checkpoint and feedback control pathways. Two mutants, rad26.T12 and rad27.T15, were selected for molecular analysis. The null allele of the rad26 gene (rad26.d) shares the phenotype reported for the "checkpoint rad" mutants rad1, rad3, rad9, rad17, and hus1, which are defective in the radiation checkpoint and in the feedback controls that ensure the order of cell cycle events. The null allele of the rad27 gene (rad27.d) defines a new class of Schizosaccharomyces pombe mutant. The rad27 complementing gene codes for a putative protein kinase that is required for cell cycle arrest after DNA damage but not for the feedback control that links mitosis to the completion of prior DNA synthesis (the same gene has recently been described by Walworth et al. (1993) as chk1). These properties are similar to those of the rad9 gene of Saccharomyces cerevisiae. A comparative analysis of the radiation responses in rad26.d, rad26.T12, and rad27.d cells has revealed the existence of two separable responses to DNA damage controlled by the "checkpoint rad" genes. The first, G2 arrest, is defective in rad27.d and rad26.d but is unaffected in rad26.T12 cells. The second response is not associated with G2 arrest after DNA damage and is defective in rad26.d and rad26.T12 but not rad27.d cells. A study of the radiation sensitivity of these mutants through the cell cycle suggests that this second response is associated with S phase and that the checkpoint rad mutants, in addition to an inability to arrest mitosis after radiation, are defective in an S phase radiation checkpoint.
为了研究确保细胞周期事件之间依赖关系的机制，以及研究DNA损伤后阻止细胞周期进程的检查点，我们分离了在检查点和反馈控制途径中存在缺陷的突变体。我们报告了11个新基因座的分离和特征，这些基因座定义了在一个或多个检查点和反馈控制途径中存在缺陷的不同类别的突变体。选择了两个突变体rad26.T12和rad27.T15进行分子分析。rad26基因的无效等位基因（rad26.d）具有与“检查点rad”突变体rad1、rad3、rad9、rad17和hus1所报道的相同表型，这些突变体在辐射检查点以及确保细胞周期事件顺序的反馈控制方面存在缺陷。rad27基因的无效等位基因（rad27.d）定义了粟酒裂殖酵母的一类新突变体。rad27互补基因编码一种假定的蛋白激酶，DNA损伤后细胞周期停滞需要该激酶，但将有丝分裂与先前DNA合成的完成联系起来的反馈控制不需要该激酶（Walworth等人（1993年）最近将同一个基因描述为chk1）。这些特性与酿酒酵母的rad9基因相似。对rad26.d、rad26.T12和rad27.d细胞辐射反应的比较分析揭示了由“检查点rad”基因控制的对DNA损伤的两种可分离的反应。第一种反应，即G2期停滞，在rad27.d和rad26.d中存在缺陷，但在rad26.T12细胞中不受影响。第二种反应与DNA损伤后的G2期停滞无关，在rad26.d和rad26.T12中存在缺陷，但在rad27.d细胞中不存在。对这些突变体在细胞周期中的辐射敏感性研究表明，这种第二种反应与S期相关，并且检查点rad突变体除了在辐射后无法阻止有丝分裂外，在S期辐射检查点也存在缺陷。
