Nurminsky D I, Nuzhdin S V, Gvozdev V A
Institute of Molecular Genetics, Russian Academy of Sciences, Moscow.
Chromosoma. 1994 Jul;103(4):277-85. doi: 10.1007/BF00352252.
The 60 kb repeats located in the distal heterochromatin of the X chromosome of Drosophila melanogaster were cloned in overlapping cosmids. These regions, designated as SCLRs, comprised the following types of repeated elements: Stellate genes, which are known to be involved in spermatogenesis; copia-like retrotransposons; LINE elements, including amplified Type I rDNA insertions; and rDNA fragments. The following steps in SCLR formation were hypothesized: insertion of mobile elements into the rDNA and Stellate gene clusters; internal tandem duplication events; recombination between the rDNA cluster and Stellate tandem repeat; and amplification of the whole SCLR structure. There are about nine SCLR copies per haploid genome, but there is approximately a twofold variation in copy number between fly stocks. The SCLR copy number differences between closely related stocks are suggested to be the result of unequal sister chromatid exchange (USCE). The restricted variation in SCLR copy number between unrelated stocks and the absence of chromosomes free of SCLRs suggests that natural selection is active in copy number maintenance.
位于黑腹果蝇X染色体远端异染色质区的60 kb重复序列被克隆到重叠黏粒中。这些区域被命名为SCLR，包含以下几种重复元件类型：已知参与精子发生的星状基因；类copia逆转座子；LINE元件，包括扩增的I型rDNA插入序列；以及rDNA片段。SCLR形成过程的以下步骤被提出假说：移动元件插入rDNA和星状基因簇；内部串联重复事件；rDNA簇与星状串联重复之间的重组；以及整个SCLR结构的扩增。单倍体基因组中约有9个SCLR拷贝，但不同果蝇品系之间的拷贝数大约有两倍的差异。亲缘关系较近的品系之间SCLR拷贝数的差异被认为是不等姐妹染色单体交换（USCE）的结果。不相关品系之间SCLR拷贝数的有限变异以及不存在不含SCLR的染色体，这表明自然选择在维持拷贝数方面发挥着作用。
