Shivram Haridha, Cawley Dillon, Christensen Shawn M
Department of Biology; University of Texas at Arlington; Arlington, TX USA.
Mob Genet Elements. 2011 Sep;1(3):169-178. doi: 10.4161/mge.1.3.18453. Epub 2011 Sep 1.
Restriction-like endonuclease (RLE) bearing non-LTR retrotransposons are site-specific elements that integrate into the genome through target primed reverse transcription (TPRT). RLE-bearing elements have been used as a model system for investigating non-LTR retrotransposon integration. R2 elements target a specific site in the 28S rDNA gene. We previously demonstrated that the two major sub-classes of R2 (R2-A and R2-D) target the R2 insertion site in an opposing manner with regard to the pairing of known DNA binding domains and bound sequences-indicating that the A- and D-clades represent independently derived modes of targeting that site. Elements have been discovered that group phylogenetically with R2 but do not target the canonical R2 site. Here we extend our earlier studies to show that a separate R2-A clade element, which targets a site other than the canonical R2 site, does so by using the N-terminal zinc fingers and Myb motifs. We further extend our targeting studies beyond R2 clade elements by investigating the ability of the N-terminal zinc fingers from the nematode NeSL-1 element to target its integration site. Our data are consistent with the use of an N-terminal DNA binding domain as one of the major targeting determinants used by RLE-bearing non-LTR retrotransposons to secure a protein subunit near the insertion site. This N-terminal DNA binding domain can undergo modifications, allowing the element to target novel sites. The binding orientation of the N-terminal domain relative to the insertion site is quite variable.
携带类限制内切核酸酶（RLE）的非长末端重复逆转座子是通过靶标引发逆转录（TPRT）整合到基因组中的位点特异性元件。携带RLE的元件已被用作研究非长末端重复逆转座子整合的模型系统。R2元件靶向28S rDNA基因中的特定位点。我们先前证明，R2的两个主要亚类（R2-A和R2-D）在已知DNA结合结构域与结合序列的配对方面以相反的方式靶向R2插入位点，这表明A和D进化枝代表了靶向该位点的独立衍生模式。已发现一些元件在系统发育上与R2聚类，但不靶向典型的R2位点。在这里，我们扩展了我们早期的研究，以表明一个单独的R2-A进化枝元件，它靶向非典型R2位点以外的位点，是通过使用N端锌指和Myb基序来实现的。我们通过研究线虫NeSL-1元件的N端锌指靶向其整合位点的能力，进一步将我们的靶向研究扩展到R2进化枝元件之外。我们的数据与使用N端DNA结合结构域作为携带RLE的非长末端重复逆转座子在插入位点附近固定蛋白质亚基的主要靶向决定因素之一相一致。这个N端DNA结合结构域可以发生修饰，使元件能够靶向新的位点。N端结构域相对于插入位点的结合方向变化很大。
