Verhage R A, Heyn J, van de Putte P, Brouwer J
Leiden Institute of Chemistry, Leiden University, The Netherlands.
Mol Gen Genet. 1997 Apr 16;254(3):284-90. doi: 10.1007/s004380050417.
Two different subpathways play a role in removal of UV-induced cyclobutane pyrimidine dimers (CPDs) by nucleotide excision repair (NER). The relatively slow global genome repair subpathway operates on all CPDs irrespective of their position in the DNA, whereas the transcription-coupled repair subpathway is responsible for the rapid removal of CPDs from transcribed strands. In Saccharomyces cerevisiae, the RAD26 gene is implicated in transcription-coupled repair. However, transcription-coupled repair is not completely absent in rad26 mutants, and therefore other gene products are possibly involved in this subpathway. Based on in vitro experiments with purified components, the transcription elongation factor S-II appeared to be a candidate for a function in transcription-coupled repair. To investigate a possible role of S-II in transcription-coupled repair in vivo in yeast, S-II null mutations were introduced into various genetic backgrounds differing in NER capacity. UV sensitivity was not altered by disruption of the S-II gene in a RAD+ (NER proficient) strain, or in rad26 (impaired in efficient transcription-coupled repair), rad7 (lacking global genome repair), or rad7 rad26 (lacking global genome repair, but having residual transcription-coupled repair capacity) mutants. Moreover, S-II did not influence the repair rate on the transcribed strand of the RPB2 gene, either in repair-proficient or in rad7 rad26 backgrounds. Hence, transcription-coupled repair is fully functional in yeast cells lacking the gene encoding S-II. Furthermore, S-II is not required for the Rad26-independent residual transcription-coupled repair in vivo.
两条不同的子途径在通过核苷酸切除修复（NER）去除紫外线诱导的环丁烷嘧啶二聚体（CPD）过程中发挥作用。相对较慢的全基因组修复子途径作用于所有CPD，无论其在DNA中的位置如何，而转录偶联修复子途径负责从转录链快速去除CPD。在酿酒酵母中，RAD26基因与转录偶联修复有关。然而，转录偶联修复在rad26突变体中并未完全缺失，因此其他基因产物可能参与了该子途径。基于对纯化成分的体外实验，转录延伸因子S-II似乎是在转录偶联修复中发挥作用的一个候选因子。为了研究S-II在酵母体内转录偶联修复中的可能作用，将S-II无效突变引入了NER能力不同的各种遗传背景中。在RAD+（NER功能正常）菌株中，或在rad26（有效转录偶联修复受损）、rad7（缺乏全基因组修复）或rad7 rad26（缺乏全基因组修复，但具有残余转录偶联修复能力）突变体中，破坏S-II基因并未改变紫外线敏感性。此外，在修复功能正常或rad7 rad26背景下，S-II对RPB2基因转录链的修复速率也没有影响。因此，在缺乏编码S-II基因的酵母细胞中，转录偶联修复功能完全正常。此外，体内不依赖Rad26的残余转录偶联修复也不需要S-II。
