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首页> 外文期刊>Molecular and Cellular Biology >The site-specific ribosomal DNA insertion element R1Bm belongs to a class of non-long-terminal-repeat retrotransposons.
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The site-specific ribosomal DNA insertion element R1Bm belongs to a class of non-long-terminal-repeat retrotransposons.

机译：位点特异性核糖体DNA插入元件R1Bm属于一类非长末端重复逆转录转座子。

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摘要

Two types of insertion elements, R1 and R2 (previously called type I and type II), are known to interrupt the 28S ribosomal genes of several insect species. In the silkmoth, Bombyx mori, each element occupies approximately 10% of the estimated 240 ribosomal DNA units, while at most only a few copies are located outside the ribosomal DNA units. We present here the complete nucleotide sequence of an R1 insertion from B. mori (R1Bm). This 5.1-kilobase element contains two overlapping open reading frames (ORFs) which together occupy 88% of its length. ORF1 is 461 amino acids in length and exhibits characteristics of retroviral gag genes. ORF2 is 1,051 amino acids in length and contains homology to reverse transcriptase-like enzymes. The analysis of 3' and 5' ends of independent isolates from the ribosomal locus supports the suggestion that R1 is still functioning as a transposable element. The precise location of the element within the genome implies that its transposition must occur with remarkable insertion sequence specificity. Comparison of the deduced amino acid sequences from six retrotransposons, R1 and R2 of B. mori, I factor and F element of Drosophila melanogaster, L1 of Mus domesticus, and Ingi of Trypanosoma brucei, reveals a relatively high level of sequence homology in the reverse transcriptase region. Like R1, these elements lack long terminal repeats. We have therefore named this class of related elements the non-long-terminal-repeat (non-LTR) retrotransposons.
机译：已知有两种插入元件，R1和R2（以前称为I型和II型）会打断几种昆虫的28S核糖体基因。在蚕蛾中，每个元素约占估计的240个核糖体DNA单元的10％，而至多只有几个拷贝位于核糖体DNA单元之外。我们在这里展示了来自桑蚕芽孢杆菌（R1Bm）的R1插入的完整核苷酸序列。这个5.1公斤的元素包含两个重叠的开放阅读框（ORF），它们共同占据其长度的88％。 ORF1的长度为461个氨基酸，并具有逆转录病毒gag基因的特征。 ORF2的长度为1,051个氨基酸，与逆转录酶样酶具有同源性。对来自核糖体基因座的独立分离物的3'和5'末端的分析支持了R1仍起转座因子作用的暗示。元素在基因组中的精确位置意味着其转座必须以显着的插入序列特异性进行。比较了六个反转录转座子，桑蚕的R1和R2，黑腹果蝇的I因子和F元素，家蝇的L1和布鲁氏锥虫的Ingi的推导氨基酸序列，发现反向序列同源性相对较高转录酶区域。像R1一样，这些元素缺少长的末端重复序列。因此，我们将这类相关元件命名为非长末端重复（non-LTR）逆转座子。

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