Brill S J, Sternglanz R
Department of Biochemistry, SUNY, Stony Brook 11794.
Cell. 1988 Jul 29;54(3):403-11. doi: 10.1016/0092-8674(88)90203-6.
Studies with yeast DNA topoisomerase mutants indicate that neither topoisomerase I nor II appears to be essential for transcription by RNA polymerase II. However, plasmids carrying transcriptionally active genes are found to be extremely negatively supercoiled when isolated from mutants lacking topoisomerase I. Supercoiling occurs during transcriptional elongation rather than during transcriptional activation. It takes place in the absence of topoisomerase I and does not seem to be dependent on topoisomerase II since it can occur at the nonpermissive temperature in a top1-top2 ts mutant. Whether this change in linking number is due to an unusual form of topoisomerase II or whether it is due to a new enzyme has yet to be determined. The results suggest that topoisomerase I is normally required to relax transcriptionally induced supercoils. A model is discussed which considers the role of topoisomerases in the movement of RNA polymerase along the DNA template.
对酵母DNA拓扑异构酶突变体的研究表明，拓扑异构酶I和II对于RNA聚合酶II的转录似乎都不是必需的。然而，当从缺乏拓扑异构酶I的突变体中分离时，携带转录活性基因的质粒被发现具有极高的负超螺旋。超螺旋发生在转录延伸过程中，而不是转录激活过程中。它在没有拓扑异构酶I的情况下发生，并且似乎不依赖于拓扑异构酶II，因为它可以在top1-top2温度敏感突变体的非允许温度下发生。这种连接数的变化是由于拓扑异构酶II的异常形式还是由于一种新的酶，还有待确定。结果表明，拓扑异构酶I通常是松弛转录诱导的超螺旋所必需的。讨论了一个模型，该模型考虑了拓扑异构酶在RNA聚合酶沿DNA模板移动中的作用。
