Mullenders L H, van Kesteren van Leeuwen A C, van Zeeland A A, Natarajan A T
Department of Radiation Genetics and Chemical Mutagenesis, State University of Leiden, The Netherlands.
Nucleic Acids Res. 1988 Nov 25;16(22):10607-22. doi: 10.1093/nar/16.22.10607.
In this study we addressed the questions as to whether repair is confined to the nuclear matrix compartment, analogous to replication and transcription and how repair events are distributed in DNA loops associated with the nuclear matrix. Pulse labelling of ultraviolet (254 nm) irradiated confluent human fibroblasts revealed that repair was preferentially located in nuclear matrix associated DNA in cells exposed to 5 J/m2. However, in cells exposed to 30 J/m2 repair approached a random distribution. The non-random distribution of repair label at 5 J/m2 was most pronounced directly after irradiation and gradually changed to a more random distribution within two hours after treatment. The results of pulse-chase experiments exclude the possibility of transient binding of repair sites to the matrix and favour the model of preferential repair of DNA sequences permanently associated with the nuclear matrix. Pronounced differences in distribution pattern of repair events in DNA loops were found among normal and UV-sensitive cell lines exposed to 5 J/m2. Repair in nuclear matrix associated DNA was 1.7 fold more efficient than in loop DNA in normal and xeroderma pigmentosum group D cells and over 3 fold in xeroderma pigmentosum group C cells. In Cockayne's syndrome fibroblasts repair in nuclear matrix DNA was found to be 2 fold less efficient than in loop DNA. This heterogeneity in distribution of repair correlates well with preferential removal of pyrimidine dimers from transcriptionally active DNA in normal and xeroderma pigmentosum group C cells and its absence in Cockayne's syndrome cells as recently reported by Mayne et al., 1988. The results suggest that Cockayne's syndrome cells have a defect in excision of UV-damage from transcriptionally active genes located proximal to the nuclear matrix. Xeroderma pigmentosum group C cells may possess a defect in DNA repair associated with chromatin regions outside transcriptionally active DNA.
在本研究中，我们探讨了修复是否局限于核基质区室（类似于复制和转录）以及修复事件如何分布于与核基质相关的DNA环中。对紫外线（254nm）照射的汇合人成纤维细胞进行脉冲标记显示，在暴露于5J/m²的细胞中，修复优先位于与核基质相关的DNA中。然而，在暴露于30J/m²的细胞中，修复接近随机分布。5J/m²时修复标记的非随机分布在照射后最明显，并在处理后两小时内逐渐变为更随机的分布。脉冲追踪实验的结果排除了修复位点与基质瞬时结合的可能性，并支持了与核基质永久相关的DNA序列优先修复的模型。在暴露于5J/m²的正常和紫外线敏感细胞系中，发现DNA环中修复事件的分布模式存在明显差异。在正常和着色性干皮病D组细胞中，与核基质相关的DNA中的修复效率比环DNA高1.7倍，在着色性干皮病C组细胞中则超过3倍。在科凯恩综合征成纤维细胞中，发现核基质DNA中的修复效率比环DNA低2倍。这种修复分布的异质性与正常和着色性干皮病C组细胞中转录活性DNA中嘧啶二聚体的优先去除以及科凯恩综合征细胞中不存在这种情况密切相关，正如梅恩等人1988年最近报道的那样。结果表明，科凯恩综合征细胞在从位于核基质近端的转录活性基因中切除紫外线损伤方面存在缺陷。着色性干皮病C组细胞可能在与转录活性DNA以外的染色质区域相关的DNA修复方面存在缺陷。
