亚东鲑基因组中Tc1-like转座子的序列歧化特征分析

Evolution analysis of Tc1-like transposon in Salmo trutta fario genome

根据鱼类Tc1-like超家族转座子的末端反向重复序列设计单引物,对西藏亚东鲑基因组进行PCR扩增、回收、克隆和测序,鉴定出亚东鲑两条长度为1 607 bp和1 473 bp的Tc1-like超家族转座子序列,命名为Tbt1和Tbt2。序列分析表明,亚东鲑Tbt1转座子左右两端分别存在一个196 nt和225 nt的末端反向重复序列(Inverted terminal repeats,ITR),在左右ITR中分别包含2个12 nt的亚末端反向重复序列(Subterminal inverted repeats,SIR);亚东鲑Tbt2转座子分别存在一个32 nt和31 nt短的ITR,其左右ITR中各仅包含1个12 nt的SIR。亚东鲑Tbt1、Tbt2转座子的转座酶编码区在进化过程中各已积累了4个和9个终止突变,两者均不能表达完整的转座酶。亚东鲑Tbt2与其它鲑科鱼类Tc1-like转座子的相似度低于30%,而与金鱼Tca2转座子的序列相似度高达98%,显示该转座子的获得可能起源于基因水平转移(horizontal gene transfer,HGT)方式。

Based on the terminal inverted repeats of Tc1-like superfamily transposons from fish, a single primer was designed to amplify similar transposon in genome of Salmo trutta fario Linnaeus. Two Tc1-like transposons sequences were amplified. The sequencing results showed that the length of the obtained fragments were 1 607 bp and 1 473 bp, named Tbt1 and Tbt2. Sequence analysis showed that there was a 196 nt and a 225 nt inverted terminal repeats （ITR） at the ends of Salmo trutta fario Tbt1, respectively. Two 12 nt Sub-terminal inverted repeats （SIR） were found among the left and right ITR. In contrast, Salmo trutta fario Tbt2 transposon had a 32 nt and 31 nt short ITRs, and the left and right ITRs each contained only one 12 nt of SIR. During evolutionary process, 4 and 9 stop codon mutations had been accumulated among transposase coding region in Salmo trutta fario Tbt1 and Tbt2, respectively, which led both transposons to lose their capacity to produce transposases. The Salmo trutta fario Tbt2 had a sequence similarity less than 30% to other salmon Tc1-like transposons, while there had a sequence identity as high as 98% to goldfish Tca2 transposon. This indicates that this transposon is very likely originated in the horizontal gene transfer mode.