Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Proc Natl Acad Sci U S A. 2011 Dec 20;108(51):20317-24. doi: 10.1073/pnas.1100278108. Epub 2011 Aug 5.
Reverse transcriptases have shaped genomes in many ways. A remarkable example of this shaping is found on telomeres of the genus Drosophila, where retrotransposons have a vital role in chromosome structure. Drosophila lacks telomerase; instead, three telomere-specific retrotransposons maintain chromosome ends. Repeated transpositions to chromosome ends produce long head to tail arrays of these elements. In both form and function, these arrays are analogous to the arrays of repeats added by telomerase to chromosomes in other organisms. Distantly related Drosophila exhibit this variant mechanism of telomere maintenance, which was established before the separation of extant Drosophila species. Nevertheless, the telomere-specific elements still have the hallmarks that characterize non-long terminal repeat (non-LTR) retrotransposons; they have also acquired characteristics associated with their roles at telomeres. These telomeric retrotransposons have shaped the Drosophila genome, but they have also been shaped by the genome. Here, we discuss ways in which these three telomere-specific retrotransposons have been modified for their roles in Drosophila chromosomes.
逆转录酶以多种方式塑造了基因组。在果蝇属的端粒上，就可以找到这种塑造的一个显著例子，在那里，逆转录转座子在染色体结构中起着至关重要的作用。果蝇缺乏端粒酶；相反，三个端粒特异性逆转录转座子维持染色体末端。重复的转位到染色体末端产生了这些元件的长头到尾的排列。在形式和功能上，这些排列与其他生物体中端粒酶添加到染色体上的重复序列的排列相似。亲缘关系较远的果蝇表现出这种不同的端粒维持机制，这种机制是在现存的果蝇物种分离之前建立的。然而，端粒特异性元件仍然具有非长末端重复（non-LTR）逆转录转座子的特征；它们还获得了与其在端粒上的作用相关的特征。这些端粒逆转录转座子塑造了果蝇的基因组，但它们也受到了基因组的影响。在这里，我们讨论了这三个端粒特异性逆转录转座子为了在果蝇染色体中发挥作用而被修饰的方式。
