Kidd S J, Glover D M
Cell. 1980 Jan;19(1):103-19. doi: 10.1016/0092-8674(80)90392-x.
We describe a cloned segment of D. melanogaster DNA (cDm219) that contains five tandemly arranged sequence units homologous to the type I insertion sequence found in the majority of 28S rRNA genes on the X chromosome. Heteroduplex studies show that two of the units have a deletion corresponding to a 1.1 kb piece of DNA close to the right-hand end of the type I insertion. Another unit has a 7.5 kb sequence (zeta) substituted for a 0.95 kb piece of DNA close to the left-hand part of the type I rDNA insertion. The two remaining units are interrupted by the Col E1 plasmid vector. There are also differences in the restriction endonuclease cleavage maps both between the units of cDm219 themselves and compared to the restriction endonuclease cleavage maps of cloned rDNA segments that contain type I insertions. Quantitation of the gel transfer hybridization of zeta element probes to restriction endonuclease digests of D. melanogaster DNA indicates there are 30--40 copies of zeta sequences distributed in seven major arrangements within the haploid genome. The hybridization of zeta and insertion sequence probes to a library of D. melanogaster DNA segments cloned in bacteriophage lambda indicates at least 4--6 copies of the zeta element could be linked to insertion sequences. The common site of in situ hybridization of zeta sequences is to the chromocentral heterochromatin of polytene chromosomes.
我们描述了一段克隆的黑腹果蝇DNA片段（cDm219），它包含五个串联排列的序列单元，这些单元与在X染色体上大多数28S rRNA基因中发现的I型插入序列同源。异源双链体研究表明，其中两个单元有一个缺失，对应于靠近I型插入序列右端的一段1.1 kb的DNA。另一个单元有一个7.5 kb的序列（ζ）取代了靠近I型rDNA插入序列左端的一段0.95 kb的DNA。剩下的两个单元被Col E1质粒载体打断。cDm219自身的单元之间以及与包含I型插入序列的克隆rDNA片段的限制性内切酶切割图谱相比，限制性内切酶切割图谱也存在差异。用ζ元件探针与黑腹果蝇DNA的限制性内切酶消化产物进行凝胶转移杂交定量分析表明，在单倍体基因组中，ζ序列有30 - 40个拷贝，分布在七种主要排列方式中。ζ和插入序列探针与克隆在λ噬菌体中的黑腹果蝇DNA片段文库杂交表明，至少有4 - 6个ζ元件拷贝可能与插入序列相连。ζ序列原位杂交的共同位点是多线染色体的染色中心异染色质。
