Buhl S N, Regan J D
Biophys J. 1974 Jul;14(7):519-27. doi: 10.1016/S0006-3495(74)85932-1.
DNA synthesized shortly after ultraviolet (UV) irradiation of human cells is made in segments that are smaller than normal, but at long times after irradiation the segments made are normal in size. Upon incubation, both the shorter and the normal segments are elongated and joined by the insertion of exogenous nucleotides to form high molecular weight DNA as in nonirradiated cells. These processes occur in normal human cells, where UV-induced pyrimidine dimers are excised, as well as in xeroderma pigmentosum (XP) cells, where dimers are not excised. The effect of caffeine on these processes was determined for both normal human and XP cells. Caffeine, which binds to denatured regions of DNA, inhibited DNA chain elongation and joining in irradiated XP cells but not in irradiated normal human or nonirradiated cells. Caffeine also caused an alteration in the ability to recover synthesis of DNA of normal size at long times after irradiation in XP cells but not in normal cells.
人类细胞经紫外线（UV）照射后不久合成的DNA是由比正常片段更小的片段组成，但在照射后的较长时间里，所合成的片段大小正常。经过温育后，较短片段和正常片段都会延长，并通过插入外源核苷酸连接起来，形成与未照射细胞中一样的高分子量DNA。这些过程在正常人类细胞中会发生，紫外线诱导的嘧啶二聚体在其中会被切除，在着色性干皮病（XP）细胞中也会发生，而在XP细胞中，二聚体不会被切除。针对正常人类细胞和XP细胞，测定了咖啡因对这些过程的影响。咖啡因会与DNA的变性区域结合，它抑制了受照射的XP细胞中的DNA链延长和连接，但在受照射的正常人类细胞或未受照射的细胞中则不会。咖啡因还导致XP细胞在照射后较长时间恢复正常大小DNA合成的能力发生改变，但在正常细胞中则不会。
