STRUCTURAL ANALYSIS OF RS447 MEGASATELLITE DNA.

我们提出了“大卫星DNA”的概念，并被广泛接受。RS447 meggassatellite DNA首次在人类4p15上被鉴定出来。476bp的单位大小串联重复约20 ~ 100次。拷贝数是高度多态的，实际上是高度可变的。通过系谱分析，60例亲代传代中有6例出现拷贝数变化。然而，这种新颖的重复序列既不是垃圾DNA，也不是自私的DNA。有一个1590bp的ORF编码一个活性去泛素酶。RS447序列在哺乳动物中是保守的。从中国仓鼠和大鼠中克隆了RS447同源物。该串联重复结构在除小鼠外的所有哺乳动物中均具有良好的保守性。因此，为了阐明RS447的结构功能及其进化过程，我们对RS447在人类和这些啮齿类动物中的同源物进行了比较研究。人类、中国仓鼠和大鼠的RS447独立拷贝测序结果表明，种内同源性超过99%，种间同源性明显较高，但种间同源性较低。这表明RS447串联重复序列在物种内通过协同进化等机制实现了同质化。目前，RS447同源物为何分散分布在小鼠基因组中仍是一个谜。我们构建了12个独立的转基因小鼠品系，同时携带人RS447作为转基因基因。这些转基因小鼠为了解RS447在小鼠体内的结构和进化提供了线索。

We proposed the concept of "megasatellite DNA" and it has been widely accepted. The RS447 megasatellite DNA was firstly identified on human 4p15. The unit size of 4746bp is tandemly repeated about 20 to 100 times. The copy number is highly polymorphic and indeed hypervariable. By pedigree analysis, 6 out of 60 parent-to-offspring transmission exhibited copy-number changes. This novel repetitive sequence is, however, neither junk nor selfish DNA. There is an ORF of 1590 bp that codes for an active deubiquitinase. The RS447 sequence is conserved in mammals. The RS447 homologs have been cloned from the Chinese hamster and rat. The tandemly repeated structure is well conserved in all the tested mammalian specied except the mouse. Thus, in order to elucidate the structural function and its evolution, the comparative studies of the RS447 homologs among human and those rodents has been conducted. Sequencing of independent copies RS447 of the human, Chinese hamster and rat indicated more than 99% identities within the species but much lower between the species although there are significantly high homologies. It implies the RS447 tandem repeat is homogenized within species by some mechanism(s) like concerted evolution. At this moment, it is an enigma why RS447 homologs is dispersed distributed in the mouse genome. We have constructed 12 independent transgenic mouse strains which tandemly carry the human RS447 as transgene. These transgenic mice should provide a clue to understand the RS447 structure and evolution in the mouse.