Beverley S M, Coderre J A, Santi D V, Schimke R T
Cell. 1984 Sep;38(2):431-9. doi: 10.1016/0092-8674(84)90498-7.
Methotrexate-resistant Leishmania tropica contain two separate regions of DNA amplification, one encoding the bifunctional thymidylate synthetase-dihydrofolate reductase (TS-DHFR) characteristic of protozoans and the other of yet unknown function. The amplified DNAs are initially found as extrachromosomal closed circular forms, which are unstable in the absence of selection. After prolonged culture in methotrexate the amplified DNAs are found as repetitive arrays associated with the chromosomal DNA fraction after CsCl-ethidium bromide density gradient centrifugation, and are stable once selection is removed. The molecular description of gene amplification in Leishmania thus closely parallels the cytological features of gene amplification in cultured mammalian cells.
对甲氨蝶呤耐药的热带利什曼原虫含有两个独立的DNA扩增区域，一个编码原生动物特有的双功能胸苷酸合成酶-二氢叶酸还原酶（TS-DHFR），另一个功能未知。扩增的DNA最初以染色体外闭合环状形式存在，在无选择条件下不稳定。在甲氨蝶呤中长时间培养后，经氯化铯-溴化乙锭密度梯度离心，扩增的DNA以与染色体DNA部分相关的重复阵列形式存在，去除选择后则稳定。因此，利什曼原虫基因扩增的分子描述与培养的哺乳动物细胞中基因扩增的细胞学特征极为相似。
