Sheen F, Lim J K, Simmons M J
Department of Genetics and Cell Biology, University of Minnesota, St. Paul 55108-1095.
Genetics. 1993 Feb;133(2):315-34. doi: 10.1093/genetics/133.2.315.
Eight independent recessive lethal mutations that occurred on derivatives of an unstable X chromosome (Uc) in Drosophila melanogaster were analyzed by a combination of genetic and molecular techniques. Seven of the mutations were localized to complementation groups in polytene chromosome bands 6E; 7A. In situ hybridization and genomic Southern analysis established that hobo transposable elements were associated with all seven of the mutations. Six mutations involved deletions of DNA, some of which were large enough to be seen cytologically, and in each case, a hobo element was inserted at the junction of the deletion's breakpoints. A seventh mutation was associated with a small inversion between 6F and 7A-B and a hobo element was inserted at one of its breakpoints. One of the mutant chromosomes had an active hobo-mediated instability, manifested by the recurrent production of mutations of the carmine (cm) locus in bands 6E5-6. This instability persisted for many generations in several sublines of an inbred stock. Two levels of instability, high and basal, were distinguished. Sublines with high instability had two hobo elements in the 6E-F region and produced cm mutations by deleting the segment between the two hobos; a single hobo element remained at the junction of the deletion breakpoints. Sublines with low instability had only one hobo element in the 6E-F region, but they also produced deletion mutations of cm. Both types of sublines also acquired hobo-mediated inversions on the X chromosome. Collectively, these results suggest that interactions between hobo elements are responsible for the instability of Uc. It is proposed that interactions between widely separated elements produce gross rearrangements that restructure the chromosome and that interactions between nearby elements cause regional instabilities manifested by the recurrence of specific mutations. These regional instabilities may arise when a copy of hobo transposes a short distance, creating a pair of hobos that can interact to produce small rearrangements.
利用遗传和分子技术相结合的方法，对果蝇中一条不稳定X染色体（Uc）的衍生物上出现的8个独立隐性致死突变进行了分析。其中7个突变定位于多线染色体带6E；7A的互补群中。原位杂交和基因组Southern分析表明，hobo转座元件与所有这7个突变有关。6个突变涉及DNA缺失，其中一些缺失大到在细胞学上可见，并且在每种情况下，一个hobo元件插入到缺失断点的连接处。第7个突变与6F和7A - B之间的一个小倒位有关，一个hobo元件插入到其一个断点处。其中一个突变染色体具有活跃的hobo介导的不稳定性，表现为在6E5 - 6带中反复产生卡红（cm）位点的突变。这种不稳定性在一个近交系的几个亚系中持续了许多代。区分出了两种水平的不稳定性，即高不稳定性和基础不稳定性。具有高不稳定性的亚系在6E - F区域有两个hobo元件，并通过缺失两个hobo之间的片段产生cm突变；在缺失断点的连接处保留一个单一的hobo元件。具有低不稳定性的亚系在6E - F区域只有一个hobo元件，但它们也产生cm的缺失突变。这两种类型的亚系在X染色体上也获得了hobo介导的倒位。总体而言，这些结果表明hobo元件之间的相互作用是Uc不稳定性的原因。有人提出，广泛分离的元件之间的相互作用会产生大规模重排，从而重组染色体，而附近元件之间的相互作用会导致区域不稳定性，表现为特定突变的反复出现。当一个hobo拷贝短距离转座时，可能会产生一对能够相互作用以产生小重排的hobo，从而引发这些区域不稳定性。
