Han Min-Jin, Xu Hong-En, Zhang Hua-Hao, Feschotte Cédric, Zhang Ze
School of Life Sciences, Chongqing University, China.
Department of Genome Oriented Bioinformatics, Wissenschaftszentrum Weihenstephan, TU Muenchen, Freising, Germany.
Genome Biol Evol. 2014 Jun 24;6(7):1748-57. doi: 10.1093/gbe/evu140.
Class 2 or DNA transposons populate the genomes of most eukaryotes and like other mobile genetic elements have a profound impact on genome evolution. Most DNA transposons belong to the cut-and-paste types, which are relatively simple elements characterized by terminal-inverted repeats (TIRs) flanking a single gene encoding a transposase. All eukaryotic cut-and-paste transposons so far described are also characterized by target site duplications (TSDs) of host DNA generated upon chromosomal insertion. Here, we report a new group of evolutionarily related DNA transposons called Spy, which also include TIRs and DDE motif-containing transposase but surprisingly do not create TSDs upon insertion. Instead, Spy transposons appear to transpose precisely between 5'-AAA and TTT-3' host nucleotides, without duplication or modification of the AAATTT target sites. Spy transposons were identified in the genomes of diverse invertebrate species based on transposase homology searches and structure-based approaches. Phylogenetic analyses indicate that Spy transposases are distantly related to IS5, ISL2EU, and PIF/Harbinger transposases. However, Spy transposons are distinct from these and other DNA transposon superfamilies by their lack of TSD and their target site preference. Our findings expand the known diversity of DNA transposons and reveal a new group of eukaryotic DDE transposases with unusual catalytic properties.
2类转座子或DNA转座子存在于大多数真核生物的基因组中，与其他移动遗传元件一样，对基因组进化有着深远影响。大多数DNA转座子属于剪切粘贴型，它们是相对简单的元件，其特征是在编码转座酶的单个基因两侧有末端反向重复序列（TIRs）。迄今为止所描述的所有真核生物剪切粘贴型转座子的特征还包括染色体插入时产生的宿主DNA靶位点重复（TSDs）。在此，我们报告了一组新的进化相关DNA转座子，称为Spy，它也包括TIRs和含DDE基序的转座酶，但令人惊讶的是，插入时不会产生TSD。相反，Spy转座子似乎精确地在5'-AAA和TTT-3'宿主核苷酸之间转座，而不会对AAATTT靶位点进行重复或修饰。基于转座酶同源性搜索和基于结构的方法，在多种无脊椎动物物种的基因组中鉴定出了Spy转座子。系统发育分析表明，Spy转座酶与IS5、ISL2EU和PIF/Harbinger转座酶有较远的亲缘关系。然而，Spy转座子因其缺乏TSD和靶位点偏好而与这些以及其他DNA转座子超家族不同。我们的发现扩展了已知的DNA转座子多样性，并揭示了一组具有异常催化特性的新型真核生物DDE转座酶。
