DNA TOPOISOMERASES AND OTHER ENZYMES AFFECTING CHROMATIN

一个主要的目的是继续研究真核生物在体内的作用， 以酵母为模型系统的DNA拓扑异构酶。 两种新酵母 拓扑异构酶，TOP3和UPRI基因的产物，将是 研究，因为将这些酶的功能重叠与 以前已知的DNA拓扑异构酶I。抑制基因，当 突变，提高各种拓扑异构酶突变体的生长，将是 克隆和分析。 编码两种爪蟾的基因 DNA拓扑异构酶I将被克隆并用于研究发育 调控这些酶的表达。 一个新的遗传系统将被用来研究 参与酵母转录抑制的各种蛋白质 沉默交配型基因座 这些基因的染色质可能与 高等真核生物中的异染色质。 此外，一种新的方法， 将使用酵母DNA复制基因。 最后， 将研究酵母十字形切割核酸内切酶。 这种酶 可能参与分解分支重组中间体 也就是霍利迪交叉口 因此，突变的影响 将研究该基因的重组。

A major aim is to continue studies on the in vivo roles of eukaryotic DNA topoisomerases using yeast as a model system. Two new yeast topoisomerases, products of the TOP3 and UPRI genes, will be investigated, as will the functional overlap of these enzymes with the previously known DNA topoisomerase I. Suppresor genes that, when mutated, improve the growth of various topoisomerase mutants, will be cloned and analyzed. The gene(s) coding for the two forms of Xenopus DNA topoisomerase I will be cloned and used to study the developmentally regulated expression of these enzymes. A novel genetic system will be employed to study interactions among the various proteins involved in transcriptional repression of the yeast silent mating-type loci. The chromatin at these genes may be similar to heterochromatin in higher eukaryotes. Also, a new approach for finding yeast DNA replication genes will be employed. Finally, the gene for a yeast cruciform-cutting endonuclease will be investigated. This enzyme may be involved in resolving the branched recombination intermediate known as the Holliday junction. Therefore, the effect of mutations in this gene on recombination will be studied.