Sikpi M O, Liu X, Lurie A G, Freedman M L
Department of Oral Diagnosis, School of Dental Medicine, University of Connecticut Health Center, Farmington 06030-1605.
Int J Radiat Biol. 1994 Feb;65(2):157-64. doi: 10.1080/09553009414550191.
The repair of damaged DNA by mammalian cells exposed to single or split doses of radiation was probed with shuttle vector pZ189. Human lymphoblast hosts who received a single 120 cGy dose 2 h before transfection with 2500 cGy-damaged pZ189 yielded a two-fold higher frequency of progeny plasmids with mutations in their supF-tRNA target genes than did unirradiated host cells. Delaying transfection for 12 h, however, reduced the mutation frequency by half versus unirradiated controls. Plasmid survival was also affected by the time between host cell irradiation and transfection. Splitting doses of 50-500 cGy into two equal fractions separated by 4 h lowered mutation frequency and increased plasmid survival compared with equivalent acute doses; increasing the interval between dose fractions to 8 h, however, lowered plasmid survival compared with acute doses. Sequence analyses of the target gene in mutant plasmids revealed increased multiple-base substitution mutations among progenies recovered from irradiated hosts, indicating enhanced excision repair. These findings support modulation of mammalian cell DNA repair by ionizing radiation, disclose the transient nature of the effect of radiation on DNA repair, and demonstrate a quantitative difference in the effectiveness of single and split doses.
利用穿梭载体pZ189对暴露于单次或分次剂量辐射的哺乳动物细胞修复受损DNA的情况进行了探究。在转染2500 cGy剂量受损的pZ189之前2小时接受单次120 cGy剂量的人淋巴母细胞宿主，其在supF - tRNA靶基因中发生突变的子代质粒频率比未受辐射的宿主细胞高出两倍。然而，将转染延迟12小时，与未受辐射的对照相比，突变频率降低了一半。质粒存活也受到宿主细胞辐射与转染之间时间的影响。与等效的急性剂量相比，将50 - 500 cGy剂量分成两个相等部分，间隔4小时，可降低突变频率并提高质粒存活；然而，与急性剂量相比，将剂量部分之间的间隔增加到8小时，则会降低质粒存活。对突变体质粒中的靶基因进行序列分析发现，从受辐射宿主中回收的子代中多碱基取代突变增加，表明切除修复增强。这些发现支持电离辐射对哺乳动物细胞DNA修复的调节作用，揭示了辐射对DNA修复影响的短暂性质，并证明了单次和分次剂量在有效性上的定量差异。
