Smith K A, Gorman P A, Stark M B, Groves R P, Stark G R
Imperial Cancer Research Fund, London, England.
Cell. 1990 Dec 21;63(6):1219-27. doi: 10.1016/0092-8674(90)90417-d.
As visualized by in situ hybridization with fluorescence detection, newly amplified CAD genes in 10(5) cell colonies are contained in multiple copies of very large regions of DNA, each tens of megabases long. The extra DNA is usually linked to the short arm of chromosome B9, which retains CAD at its normal site. The widely spaced genes are often interspersed with new G-negative regions. Individual cells within a clone have highly variable numbers of CAD genes (range 2-15). When resistant clones are examined later, at the 10(15) cell stage, the amplified genes are usually found in much more condensed structures. We propose that, in the initial event of CAD gene amplification, much of the short arm is transferred from one B9 chromosome to another. In subsequent cell cycles this initial duplication expands rapidly through unequal but homologous sister chromatid exchanges. Relatively rare secondary events lead to more condensed structures.
通过荧光检测原位杂交观察到，在10⁵个细胞集落中新扩增的CAD基因包含在多个非常大的DNA区域的多拷贝中，每个区域长达数十兆碱基。额外的DNA通常与B9染色体的短臂相连，而CAD基因仍保留在其正常位置。间隔广泛的基因常常散布着新的G阴性区域。克隆内的单个细胞中CAD基因的数量变化很大（范围为2 - 15）。当在10¹⁵个细胞阶段后期检查抗性克隆时，扩增的基因通常以更为浓缩的结构存在。我们提出，在CAD基因扩增的初始事件中，大部分短臂从一条B9染色体转移到了另一条B9染色体上。在随后的细胞周期中，这种初始复制通过不等但同源的姐妹染色单体交换迅速扩展。相对罕见的二次事件导致形成更为浓缩的结构。
