Slotkin R Keith, Freeling Michael, Lisch Damon
Department of Plant and Microbial Biology, 111 Koshland Hall, University of California Berkeley, Berkeley, California 94720, USA.
Nat Genet. 2005 Jun;37(6):641-4. doi: 10.1038/ng1576. Epub 2005 May 22.
It has been suggested that gene silencing evolved as a defense against genomic parasites such as transposons. This idea is based on analysis of mutations that reactivate transposons that are stably silenced: they affect maintenance rather than initiation of silencing. Here we describe the cloning and characterization of a naturally occurring locus able to heritably silence the otherwise highly active MuDR transposon in maize. This locus, Mu killer (Muk), results from the inverted duplication of a partially deleted autonomous MuDR element located at the breakpoint of a genomic deletion. Muk produces a hybrid hairpin transcript that is processed into small RNAs, which are amplified when the target MuDR transcript is present. Muk provides the first example of a naturally occurring transposon derivative capable of initiating the heritable silencing of an active transposon family. Further, transposon-generated inverted duplications may be important for the generation of double-stranded RNAs used in gene silencing.
有人提出，基因沉默是作为一种针对转座子等基因组寄生虫的防御机制而进化的。这一观点基于对使稳定沉默的转座子重新激活的突变的分析：这些突变影响的是沉默的维持而非起始。在此，我们描述了一个能够遗传性地沉默玉米中原本高度活跃的MuDR转座子的天然位点的克隆与特性分析。这个位点，即Mu杀手（Muk），是由位于基因组缺失断点处的一个部分缺失的自主MuDR元件的反向重复产生的。Muk产生一种杂合发夹转录本，该转录本被加工成小RNA，当存在靶标MuDR转录本时，这些小RNA会被扩增。Muk提供了首个能够起始活跃转座子家族遗传性沉默的天然转座子衍生物的实例。此外，转座子产生的反向重复可能对于用于基因沉默的双链RNA的产生很重要。
