ENZYMES INVOLVED IN DNA REPAIR AND MEIOSIS

从DNA修复和重组的研究中，很明显，核酸酶 在这两个过程中都发挥着重要作用。在酿酒酵母中 RAD52基因对DNA双链断裂的修复是必不可少的 (DSB)、有丝分裂重组和成功完成减数分裂。 尽管RAD52的功能仍不清楚，但RAD52可能在 控制72kD核酸酶(RhoNUC)的水平。来自西方的印迹 分析表明，在rad52突变体中，RhoNUC的水平大大降低 提示该核酸酶受RAD52调控。基因 编码RhoNUC(RNC1)的基因已被克隆和测序。平均值分析 将编码RhoNUC的基因定位在XI号染色体上。考试的结果 推导的一级序列表明，RhoNUC是一个嵌合蛋白，与 与ras/Rho显示广泛同源性的N-末端区域 GTP结合蛋白的超家族，而C末端似乎编码 核酸酶的功能。因此，这个蛋白质被命名为RhoNUC，意思是Rho- 相关核酸酶。对RNC1：：LacZ基因融合的分析表明 RAD52对RhoNUC的调控不发生在转录水平 这表明控制处于翻译后水平。虽然 RNC1的过表达不会产生显著的遗传表型， 过度表达确实会导致细胞增大，并出现细胞核 放大并弥漫。有趣的是，携带这两种基因缺失的菌株 RAD52和RNC1具有接近野生型水平的直接重复重组 当在质粒上或在染色体上进行测量时(菌株携带 只有RAD52的缺失显示重组水平约为100- 比野生型低)。从这些观察来看，我们认为 RhoNUC代表了一类新发现的蛋白质，它既表现出 细胞信号功能(G蛋白活性)与DNA代谢 活性(参与重组的核酸酶活性)。

From studies of DNA repair and recombination, it is apparent that nucleases play a major role in both of these processes. In the yeast S. cerevisiae the RAD52 gene is essential for the repair of DNA double-strand breaks (DSB), mitotic recombination and for the successful completion of meiosis. Although the function of RAD52 remains unclear, RAD52 may play a role in controlling the levels of a 72 kD nuclease (RhoNUC). From Western blot analysis, the levels of RhoNUC are greatly decreased in rad52 mutants suggesting that this nuclease is under the control of RAD52. The gene encoding RhoNUC (RNC1) has been cloned and sequenced. OFAGE analysis placed the gene encoding RhoNUC on chromosome XI. Examination of the deduced primary sequence reveals that RhoNUC is a chimeric protein with the N-terminal region exhibiting extensive homology with the ras/rho superfamily of GTP binding proteins while the C-terminus appears to encode the nuclease function. Hence, this protein has been named RhoNUC for rho- associated nuclease. Analysis of RNC1::lacZ gene fusions reveals that the control of RhoNUC by RAD52 does not occur at the level of transcription suggesting that the control is at the post-translational level. Although overexpression of RNC1 yields no significant genetic phenotype, the overexpression does cause the cells to enlarge and their nuclei appear enlarged and diffuse. Interestingly, strains carrying deletions for both RAD52 and RNC1 have nearly wild-type levels of direct repeat recombination when measured either on plasmids or on the chromosome (strains carrying only a deletion of RAD52 exhibit recombination levels approximately 100- fold lower than wild-type). From these observations, we believe that RhoNUC represents a newly identified class of proteins exhibiting both a cellular signalling function (G-protein activity) and a DNA metabolic activity (nuclease activity involved in recombination).