Akagi H, Yokozeki Y, Inagaki A, Mori K, Fujimura T
Department of Biological Production, Faculty of Bioresource Sciences, Akita Prefectural University, Akita 010-0195, Japan.
Mol Genet Genomics. 2001 Nov;266(3):471-80. doi: 10.1007/s004380100563.
We have isolated a new family of mobile elements, Micron, which occur within microsatellites dispersed throughout the rice (Oryza sativa) genome. The first of these segments, Micron 001, was found in a microsatellite consisting of a (TA)n sequence upstream of the rice phytochrome A (phyA) gene. PCR analysis of related rice species suggests that Micron 001 integrated into this microsatellite locus prior to the divergence of the two wild species O. rufipogon and O. barthii from a common ancestor. Micron elements are short (393-bp), possess subterminal inverted repeats and the single strands have the potential to form stable secondary structures via several internal repeats. Aside from the absence of terminal inverted repeats, these characteristics resemble those of MITEs (Miniature Inverted-Repeat Transposable Elements). We estimate that 100-200 copies of Micron-related sequences are present in the rice nuclear genome, while the chloroplast and mitochondrial genomes lack this sequence. Nineteen homologs of Micron 001 exhibited extremely high nucleotide sequence conservation (greater than 90%), suggesting a recent spread of Micron elements within the genus Oryza. Surprisingly, nucleotide sequence alignments showed that all of the Micron elements are flanked on both sides by microsatellite sequence consisting mainly of (TA)n. Twenty-three elements were mapped to seven separate chromosomes. Therefore Micron elements form a family of dispersed, highly conserved repeats. This is the first report of a transposable element that targets microsatellite loci.
我们分离出了一个新的可移动元件家族——Micron，它们存在于遍布水稻（Oryza sativa）基因组的微卫星序列中。其中的第一个片段Micron 001，是在水稻光敏色素A（phyA）基因上游一个由（TA）n序列组成的微卫星中发现的。对相关水稻品种的PCR分析表明，Micron 001在两个野生种——来自共同祖先的野生稻（O. rufipogon）和非洲栽培稻（O. barthii）分化之前就已整合到这个微卫星位点中。Micron元件很短（393 bp），具有亚末端反向重复序列，单链有通过几个内部重复序列形成稳定二级结构的潜力。除了没有末端反向重复序列外，这些特征与微型反向重复转座元件（MITEs）相似。我们估计水稻核基因组中存在100 - 200个与Micron相关的序列拷贝，而叶绿体和线粒体基因组中则缺乏该序列。Micron 001的19个同源物表现出极高的核苷酸序列保守性（大于90%），这表明Micron元件在稻属内是最近才扩散的。令人惊讶的是，核苷酸序列比对显示，所有的Micron元件两侧都主要由（TA）n组成的微卫星序列所环绕。23个元件被定位到7条不同的染色体上。因此，Micron元件形成了一个分散的、高度保守的重复序列家族。这是关于一个靶向微卫星位点的转座元件的首次报道。
