Otto E, Young J E, Maroni G
Proc Natl Acad Sci U S A. 1986 Aug;83(16):6025-9. doi: 10.1073/pnas.83.16.6025.
A strain of cadmium-resistant Drosophila containing a chromosomal duplication of the metallothionein gene was isolated. This duplication is stably inherited in the absence of selective pressure, and larvae homozygous for it can produce approximately twice as much metallothionein RNA as wild-type larvae. The entire duplication was cloned within a 5.7-kilobase fragment; this fragment contained a direct, tandem repeat of 2.2 kilobases of DNA: 228 bases of 5' flanking DNA, the entire transcription unit, and 1.4 kilobases of 3' flanking sequences. The 3' region of the first repeated unit is joined to the 5' region of the second unit by a 6-base-pair segment we define as the novel joint. This joint forms part of a 10-base-pair inverted repeat of a segment within the 3' region of the first unit. Comparison of the sequences of the 5' and 3' boundaries revealed no extensive regions of similarity at a position corresponding to the novel joint, thus suggesting that a mechanism other than homologous recombination was involved in the origin of this duplication.
分离出了一种含有金属硫蛋白基因染色体重复的抗镉果蝇品系。这种重复在没有选择压力的情况下能够稳定遗传，并且纯合的幼虫产生的金属硫蛋白RNA量大约是野生型幼虫的两倍。整个重复序列被克隆到一个5.7千碱基的片段中；该片段包含一段2.2千碱基DNA的直接串联重复序列：228个碱基的5'侧翼DNA、整个转录单元以及1.4千碱基的3'侧翼序列。第一个重复单元的3'区域通过一个我们定义为新接头的6碱基对片段与第二个单元的5'区域相连。这个接头构成了第一个单元3'区域内一个片段的10碱基对反向重复序列的一部分。5'和3'边界序列的比较显示，在与新接头对应的位置没有广泛的相似区域，因此表明这种重复的起源涉及到同源重组以外的机制。
