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 基因是修复DNA双链断裂所必需的，有丝分裂 重组和成功完成减数分裂。72kD 核酸酶(RhoNUC)已被鉴定并纯化。在RAD52中 突变体，RhoNuc的水平大大降低，这表明这 核酸酶由RAD52控制。编码RhoNUC的基因已经被 克隆并测序。Fage分析将编码RhoNUC的基因 (RNC1)位于染色体XI上。对推导出的一级序列的检验 DNA序列分析表明，RhoNUC是一种嵌合蛋白。N端子 该蛋白区域与ras/rho高度同源。 GTP结合蛋白的超家族，而C末端似乎编码 蛋白质的核酸酶部分。因此，这种蛋白质被命名为 RhoNUC代表Rho相关核酸酶。通过利用RNC1：：LacZ融合 构建在包含野生型RAD52基因或 完全删除RAD52，看来RhoNUC是由RAD52控制的 是后翻译的。RNC1基因的过度表达不会产生明显的结果 表型。然而，同时携带RNC1和RAD52缺失的菌株具有 直接重复重组的近乎野生型水平 在质粒上或在染色体上(仅携带RAD52缺失的菌株 重组水平比野生型低约100倍)。 根据这些观察，我们认为RhoNUC代表了一种新的 一类既具有细胞信号功能又具有细胞信号功能的蛋白质 (G蛋白活性)和DNA代谢活性(核酸酶活性 参与重组)。

From studies of DNA repair and recombination, it is apparent that nucleases play a major role in both of these processes. In S. cerevisiae the RAD52 gene is essential for the repair of DNA double-strand breaks, mitotic recombination and for the successful completion of meiosis. A 72 kD nuclease (RhoNUC) has been identified and subsequently purified. In rad52 mutants, levels of RhoNuc are greatly decreased suggesting that this nuclease is under the control of RAD52. The gene encoding RhoNUC has been cloned and sequenced. OFAGE analysis places the gene encoding RhoNUC (RNC1) on chromosome XI. Examination of the deduced primary sequence from the DNA sequence reveals that RhoNUC is a chimeric protein. The N-terminal region of the protein shares a high degree of homology with the ras/rho superfamily of GTP binding proteins while the C-terminal appears to encode the nuclease portion of the protein. Hence, this protein has been named RhoNUC for rho-associated nuclease. By utilizing a RNC1::lacZ fusion construct in strains that either contain a wild type RAD52 gene or a complete deletion of RAD52, it appears that the control of RhoNUC by RAD52 is post-translational. Overexpression of RNC1 gene yields no observable phenotype. However, strains carrying deletions of both RNC1 and RAD52 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).