Bill C A, Nickoloff J A
Department of Molecular Genetics and Microbiology, University of New Mexico School of Medicine, 915 Camino de Salud, Albuquerque, NM 87131, USA.
Mutat Res. 2001 Nov 1;487(1-2):41-50. doi: 10.1016/s0921-8777(01)00101-x.
Recombination is enhanced by transcription and by DNA damage caused by ultraviolet light (UV). Recombination between direct repeats can occur by gene conversion without an associated crossover, which maintains the gross repeat structure. There are several possible mechanisms that delete one repeat and the intervening sequences (gene conversion associated with a crossover, unequal sister chromatid exchange, and single-strand annealing). We examined transcription-enhanced spontaneous recombination, and UV-induced recombination between neomycin (neo) direct repeats. One neo gene was driven by the inducible MMTV promoter. Multiple (silent) markers in the second neo gene were used to map conversion tracts. These markers are thought to inhibit spontaneous recombination, and our data suggest that this inhibition is partially overcome by high level transcription. Recombination was stimulated by transcription and by UV doses of 6-12J/m(2), but not by 18J/m(2). About 70% of spontaneous and UV-induced products were deletions. In contrast, only 3% of DSB-induced products were deletions. We propose that these product spectra differ because spontaneous and UV-induced recombination is replication-dependent, whereas DSB-induced recombination is replication-independent.
转录以及紫外线（UV）造成的DNA损伤会增强重组。同向重复序列之间的重组可通过基因转换发生，而不伴有相关的交叉，这维持了重复序列的总体结构。存在几种可能的机制可删除一个重复序列及中间序列（与交叉相关的基因转换、不等姐妹染色单体交换和单链退火）。我们研究了转录增强的自发重组以及紫外线诱导的新霉素（neo）同向重复序列之间的重组。一个neo基因由可诱导的MMTV启动子驱动。第二个neo基因中的多个（沉默）标记用于绘制转换片段。这些标记被认为可抑制自发重组，我们的数据表明这种抑制可被高水平转录部分克服。转录以及6 - 12J/m(2)的紫外线剂量可刺激重组，但18J/m(2)的剂量则不能。约70%的自发和紫外线诱导产物为缺失型。相比之下，双链断裂（DSB）诱导产物中只有3%为缺失型。我们认为这些产物谱不同是因为自发和紫外线诱导的重组依赖复制，而DSB诱导的重组不依赖复制。
