Kitamura K, Hashida S N, Mikami T, Kishima Y
Laboratory of Genetic Engineering, Faculty of Agriculture, Hokkaido University, Sapporo, Japan.
Plant Mol Biol. 2001 Nov;47(4):475-90. doi: 10.1023/a:1011892003996.
We identified eight independent Tam3 copies residing in the same Antirrhinum majus genome. All the copies showed excision at 15 degrees C, but not at 25 degrees C. Under conditions promoting excision, each copy appeared to transpose in the leaves and flower lobes with a nearly constant frequency, whereas individual transposition abilities varied widely: the most active copy had an excision frequency more than 100-fold greater than that of the least active one. Despite the different transposition abilities, the structures of the eight Tam3 copies were almost identical. These results made it clear that the transpositional ability of Tam3 is regulated by chromosomal position, but they do not imply position-dependent transposase activity. The position effect of the Tam3 transposition was found to be correlated to the methylation state of the copy's end regions: DNA methylation in the Tam3 end regions tended to suppress the excision activity, and the degree of methylation was dependent on the chromosomal position. Our results also provide evidence of de novo methylation provoked by transposition of the endogenous element. We propose a mechanism of transpositional regulation of plant transposons that responds to the degree of methylation as determined by chromosomal position.
我们在同一金鱼草基因组中鉴定出八个独立的Tam3拷贝。所有拷贝在15摄氏度时均发生切除，但在25摄氏度时则不会。在促进切除的条件下，每个拷贝似乎都以几乎恒定的频率在叶片和花裂片中转座，然而个体转座能力差异很大：最活跃的拷贝的切除频率比最不活跃的拷贝高100倍以上。尽管转座能力不同，但八个Tam3拷贝的结构几乎相同。这些结果表明，Tam3的转座能力受染色体位置调控，但并不意味着转座酶活性依赖于位置。发现Tam3转座的位置效应与拷贝末端区域的甲基化状态相关：Tam3末端区域的DNA甲基化倾向于抑制切除活性，且甲基化程度取决于染色体位置。我们的结果还提供了内源性元件转座引发从头甲基化的证据。我们提出了一种植物转座子转座调控机制，该机制对由染色体位置决定的甲基化程度作出反应。
