Gaddini L, Pelliccia F, Limongi M Z, Rocchi A
Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, Rome, Italy.
Mutagenesis. 1995 May;10(3):257-60. doi: 10.1093/mutage/10.3.257.
This paper reports the results of an investigation into the relationship between common fragile sites and sister chromatid exchanges (SCE). Human leukocyte cultures were grown in two different media, one complete (RPMI 1640) and one deficient in folic acid and thymidine (199M). Some of the cultures were treated with DAPI, a non-intercalating compound which binds preferentially to the AT bases of DNA and is capable of inducing fragile sites. Bromodeoxyuridine (BrdU) was added to all the cultures for SCE analysis. Chromomycin A3 was used for mapping lesions and SCEs by R-banding. A total of 400 cells was examined. The main results show that: BrdU, probably by re-equilibrating the unbalanced nucleotide pool of the 199 culture medium, interferes with the synergism between this culture medium and DAPI in inducing the expression of fragile sites; the SCE frequency per cell is not increased by DAPI in both culture media, therefore this compound does not seem to cause any damage to the DNA and seems merely to act by inhibiting the normal condensation of a subset of fragile sites that possess DAPI-specific base sequences; even in the absence of chromosomal lesions, the fragile sites are significantly preferred as SCE sites to non-fragile sites, whereas in the presence of a lesion, both fragile and non-fragile sites have the same likelihood of undergoing SCE. All this indicates that the presence of a lesion strongly favours SCE formation and that common fragile sites are probably chromosome regions preferentially damaged during the S phase.
本文报道了一项关于常见脆性位点与姐妹染色单体交换（SCE）之间关系的调查结果。人类白细胞培养物在两种不同的培养基中生长，一种是完全培养基（RPMI 1640），另一种是缺乏叶酸和胸腺嘧啶的培养基（199M）。部分培养物用DAPI处理，DAPI是一种非嵌入性化合物，它优先结合DNA的AT碱基并能够诱导脆性位点。向所有培养物中添加溴脱氧尿苷（BrdU）用于SCE分析。使用放线菌素A3通过R显带对损伤和SCE进行定位。共检查了400个细胞。主要结果表明：BrdU可能通过重新平衡199培养基中不平衡的核苷酸库，干扰了该培养基与DAPI在诱导脆性位点表达方面的协同作用；在两种培养基中，DAPI均未增加每个细胞的SCE频率，因此该化合物似乎不会对DNA造成任何损伤，似乎只是通过抑制具有DAPI特异性碱基序列的一部分脆性位点的正常凝聚来发挥作用；即使在没有染色体损伤的情况下，脆性位点作为SCE位点也比非脆性位点更受青睐，而在存在损伤的情况下，脆性和非脆性位点发生SCE的可能性相同。所有这些表明，损伤的存在强烈促进SCE的形成，并且常见脆性位点可能是在S期优先受损的染色体区域。
