Birth of a retroposon:: The Twin SINE family from the vector mosquito Culex pipiens may have originated from a dimeric tRNA precursor
Birth of a retroposon:: The Twin SINE family from the vector mosquito Culex pipiens may have originated from a dimeric tRNA precursor
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DOI：
10.1093/oxfordjournals.molbev.a003721
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发表时间：
2001-01-01
影响因子：
10.7
通讯作者：
Mouchès, C
中科院分区：
文献类型：
--
作者：
Feschotte, C;Fourrier, N;Mouchès, C
西内斯是在许多真核生物基因组中发现的短的散布的重复元件，并且被认为通过逆转录来繁殖。迄今为止，几乎所有的西内斯都具有由5'端tRNA相关区域和随后的tRNA无关区域组成的复合结构。在这里，我们描述了一种新的类型的tRNA衍生的西内斯从蚊子库蚊的基因组。这些元件，称为双胞胎，类似于220 bp长，每个单倍体基因组重复约500个拷贝。与目前所描述的其它tRNA-SINE相比，Tcr，ins具有独特的结构。它们由两个tRNA（Arg）相关区域组成，由39 bp的间隔区隔开。其他与tRNA无关的序列包括位于左侧tRNA样区之前的5-bp前导序列和位于右侧tRNA样区下游的短尾序列。该3'尾部是10-bp序列，其以TTTT基序结束，随后是可变长度的polyA段。右边的tRNA样单位也含有一个16 bp的序列，它在左边的单位中是不存在的，似乎正好位于祖先反密码子茎中的一个预期为核tRNA内含子的位置。根据这种奇异的结构，我们假设Twin SINE家族起源于含有两个tRNA序列的未加工的聚合酶III转录物。我们认为，这种双顺反子转录物获得的一些特殊性质，如polyA尾和3'茎环二级结构，通过增加其被C. pipiens基因组。
SINEs are short interspersed repetitive elements found in many eukaryotic genomes and are believed to propagate by retroposition. Almost all SINEs reported to date have a composite structure made of a 5' tRNA-related region followed by a tRNA-unrelated region. Here, we describe a new type of tRNA-derived SINEs from the genome of the mosquito Culex pipiens. These elements, called Twins, are similar to 220 bp long and reiterated at approximately 500 copies per haploid genome. Tcr,ins have a unique structure compared with other tRNA-SINEs described so far. They consist of two tRNA(Arg)-related regions separated by a 39-bp spacer. Other tRNA-unrelated sequences include a 5-bp leader preceding the left tRNA-like unit and a short trailer located downstream of the right tRNA-like region. This 3' trailer is a 10-bp sequence that is ended by a TTTT motif and followed by a polyA tract of variable length. The right tRNA-like unit also contains a 16-bp sequence which is absent in the left one and appears to be located in the ancestral anticodon stem precisely at a position expected for a nuclear tRNA intron. According to this singular structure, we hypothesize that the Twin SINE family originated from an unprocessed polymerase ill transcript containing two tRNA sequences. We suggest that some peculiar properties acquired by this dicistronic transcript, such as a polyA tail and a 3' stem-loop secondary structure, promote its retroposition by increasing its chances of being recognized by a reverse transcriptase encoded elsewhere in the C. pipiens genome.