Structure and Function of Tpn transposable elements in the Japanese morning glory

已知日本牵牛花的一些突变是由转座因子的插入引起的体细胞和胚细胞不稳定。到目前为止，引起突变表型的转座因子已经从几个基因中分离出来。所有这些元素都属于En/Spm家族。它们都携带共同的28 bp末端反向重复序列（TIR）和亚末端区域与许多重复。这些具有共同末端序列的转座因子被称为Tpn 1家族。所有这些都被认为是非自主元件，这些元件在可变等位基因中被自主元件调动。Tpn 1家族的拷贝数估计在每个单倍体基因组500至1000个拷贝之间。用亚末端探针共分离到200多个Tpn克隆，其中128个克隆经酶切图谱鉴定可分为30类。对30个群体中19个具有代表性的Tpn克隆进行了全序列测定。所有Tpn的5 '端共有区（包括TIR区、亚末端区和非重复区）比3'端共有区长得多。有趣的是，它们的Tpns的内部序列在组间差异很大，并且来自宿主基因序列。Tpn 1家族的另一个有趣的特点是每个5'和3'共同序列的系统发育树没有形成平行关系。通过5 ′-亚末端区域和内部序列之间的连接，不同群体之间的重组事件发生在3 ′-区域。我们推测了Tpns在进化过程中整合宿主基因序列的机制。Tpns的3'端突出末端主要作为模板侵入同源宿主基因中，发生Abortive Gap Repair事件。

Some mutations of the Japanese morning glory were known to be unstable somatically and germinally as caused by insertions of transposable elements. Until now, transposable elements that cause mutable phenotypes have been isolated from several genes. All of these elements belong to the En/Spm family by their structures. They all carried common 28-bp terminal inverted repeats (TIRs) and subterminal regions with many repeats. These transposable elements with common terminal sequences are termed Tpn1 family. All of them thought to be nonautonomous elements and these elements in mutable alleles are mobilized by autonoumous elements. The copy number of Tpn1 family was estimated between 500 and 1000 copies per haploid genome. Using probe of subterminal regions, we isolated more than 200 Tpn clones, and 128 clones were classified into 30 groups by their restriction maps. We decided the complete sequences of 19 representative Tpn clones from 30 groups. The comparison of their common regions among all Tpns indicates that the 5'-common regions including TIR, subterminal and non-repetitive regions are much longer than 3'-common regions. Interestingly, their internal sequences of Tpns were quite different among groups and were derived from host gene sequences. Another interesting feature of the Tpn1 family is the phylogenetic trees of each 5' and 3'common sequences did not make parallel relationships. By the linkage between 5'-subterminal regions and internal sequences, recombination events between different groups occurred in 3'-regions. We deduced a mechanism that Tpns incorporated host gene sequences in process of evolution from these findings. 3' protruding ends of Tpns mainly invades into homologous host genes as templates when Abortive Gap Repair events were occurred.