Christman M F, Dietrich F S, Fink G R
Whitehead Institute for Biomedical Research, Nine Cambridge Center, Massachusetts 02142.
Cell. 1988 Nov 4;55(3):413-25. doi: 10.1016/0092-8674(88)90027-x.
We have found that mitotic recombination within the S. cerevisiae rDNA cluster (200 tandemly repeated 9.1 kb units) is strongly suppressed and that this suppression requires the combined action of DNA topoisomerases I and II. Strains with a null mutation in the TOP1 gene (encoding topoisomerase I) or a ts mutation in the TOP2 gene (encoding topoisomerase II) grown at a semipermissive temperature show 50- to 200-fold higher frequencies of mitotic recombination in rDNA relative to TOP+ controls. Suppression of recombination is specific to the rDNA because the recombination frequency at another tandem array, the CUP1 locus, at a simple HIS4 duplication, or among dispersed repeats (MAT and HML or HMR) is not elevated in top1 or top2 mutants. The high frequency of mitotic recombination within the rDNA cluster in topoisomerase mutants shows that both TOP1 and TOP2 are required for suppression of recombination in this region of the genome.
我们发现，酿酒酵母rDNA簇（200个串联重复的9.1 kb单元）内的有丝分裂重组受到强烈抑制，且这种抑制需要DNA拓扑异构酶I和II的共同作用。在半允许温度下生长的TOP1基因（编码拓扑异构酶I）发生无效突变或TOP2基因（编码拓扑异构酶II）发生温度敏感型突变的菌株，相对于TOP+对照，rDNA中有丝分裂重组频率高50至200倍。重组抑制对rDNA具有特异性，因为在另一个串联阵列CUP1位点、简单的HIS4重复处或分散重复序列（MAT和HML或HMR）之间的重组频率在top1或top2突变体中并未升高。拓扑异构酶突变体中rDNA簇内有丝分裂重组的高频表明，TOP1和TOP2都是基因组该区域重组抑制所必需的。
