Garvey E P, Santi D V
Science. 1986 Aug 1;233(4763):535-40. doi: 10.1126/science.3726545.
The relative stability of amplified DNA in drug-resistant Leishmania major was previously reported to be dependent on location, that is, unstable amplified DNA was extrachromosomal and stable amplified DNA was chromosomal. Leishmanial chromosomes have now been directly examined by means of orthogonal-field-alternation gel electrophoresis (OFAGE). The amplified DNA's in three resistant cell lines displayed unusual migration and were clearly extrachromosomal, regardless of whether the amplified DNA's were stable or unstable. Thus, contrary to conclusions from earlier studies of drug resistance in cultured animal cells, stable amplified DNA in Leishmania can be extrachromosomal. In addition, these amplified DNA's were shown to be circular on the basis of their resistance to exonuclease III digestion and their behavior on OFAGE. Their mobility was also greatly changed after treatment with topoisomerase II, suggesting that the amplified DNA's were either supercoiled or concatenated circles.
先前有报道称，抗药型硕大利什曼原虫中扩增DNA的相对稳定性取决于其位置，即不稳定的扩增DNA是染色体外的，而稳定的扩增DNA是染色体上的。现在已经通过正交交变电场凝胶电泳（OFAGE）直接检测了利什曼原虫的染色体。三种抗性细胞系中的扩增DNA呈现出异常迁移，并且明显是染色体外的，无论扩增DNA是稳定的还是不稳定的。因此，与早期对培养动物细胞抗药性研究的结论相反，利什曼原虫中稳定的扩增DNA可以是染色体外的。此外，根据这些扩增DNA对外切核酸酶III消化的抗性及其在OFAGE上的行为，表明它们是环状的。用拓扑异构酶II处理后，它们的迁移率也发生了很大变化，这表明扩增DNA要么是超螺旋的，要么是连环环。
