Bassi L, Palitti F, Mosesso P, Natarajan A T
Dipartimento di Agrobiologia e Agrochimica Università degli Studi della Tuscia, Viterbo, Italy.
Mutagenesis. 1998 May;13(3):257-61. doi: 10.1093/mutage/13.3.257.
The distribution of camptothecin (CPT)-induced break points in late S or G2 phase of the cell cycle observed in Chinese hamster chromosomes was analysed in 400 metaphases. Contrary to expectation, they were not localized in the heterochromatic regions, suggesting that these chromatid-type aberrations arise by a mechanism which does not involve collision of the CPT-trapped 'cleavable complex' with the replication fork. Since many break points mapped more frequently to light bands (DAPI negative) than dark bands (DAPI positive) with a frequency of 73 and 15% respectively, it could be argued that the presence of the CPT-trapped 'cleavable complex' probably interferes with chromatin condensation. In fact, the euchromatic regions, which are expected to be more actively condensed in G2 phase, were more involved in chromosomal damage. These results do not completely confirm the idea that some residual DNA synthesis occurring in G2 is responsible for the G2 clastogenic effects of CPT as the heterochromatic regions should, in this case, be more involved.
在400个中期相中分析了喜树碱（CPT）诱导的中国仓鼠染色体在细胞周期S期晚期或G2期的断点分布。与预期相反，它们并不定位于异染色质区域，这表明这些染色单体型畸变是通过一种不涉及CPT捕获的“可切割复合物”与复制叉碰撞的机制产生的。由于许多断点分别以73%和15%的频率更频繁地映射到浅带（DAPI阴性）而非深带（DAPI阳性），可以认为CPT捕获的“可切割复合物”的存在可能会干扰染色质凝聚。事实上，预计在G2期更活跃凝聚的常染色质区域更多地参与了染色体损伤。这些结果并未完全证实G2期发生的一些残留DNA合成是CPT的G2期致断裂效应的原因这一观点，因为在这种情况下异染色质区域应该更多地参与其中。
