Whalen J H, Grigliatti T A
Department of Zoology, University of British Columbia, Vancouver, Canada.
Mol Gen Genet. 1998 Dec;260(5):401-9. doi: 10.1007/s004380050910.
The nomad element was identified as a retrovirus-like transposon in Drosophila melanogaster. DNA sequence analysis showed that the nomad element contains three long ORFs that are similar to the gag, pol and env genes of retrovirus- and the copia-like elements of D. melanogaster. The nomad element terminates with 519-bp terminal repeats, each of which contains eukaryotic consensus transcription initiation and termination signals. nomad elements are located at approximately 10-15 sites within the euchromatic arms of the genome and at the chromocenter, as shown by in situ hybridization. The host DNA sequence TANA was found to be duplicated on each side of the nomad element and appears to be a preferential target site for insertion of nomad elements. Analysis of the zinc finger motif in the pol gene product of retrotransposons known to have target site preference suggests involvement of the integrase subunit in target site selection for those retrotransposons that display insert site specificity. A comparison of the predicted amino acid sequence of the pol-like genes of several known retrotransposons was made and the phylogenetic relationship between nomad and other retrovirus-like mobile elements was determined. It was clear from this conceptual protein analysis and from analysis of their structural characteristics that retrotransposons of the gypsy class can be generally classified as members of one of two distinct groups. The phylogenetic relationships of these groups are also discussed.
游牧元件在黑腹果蝇中被鉴定为一种逆转录病毒样转座子。DNA序列分析表明，游牧元件包含三个长开放阅读框，它们与逆转录病毒的gag、pol和env基因以及黑腹果蝇的类copia元件相似。游牧元件以519个碱基对的末端重复序列终止，每个末端重复序列都包含真核生物共有的转录起始和终止信号。原位杂交显示，游牧元件位于基因组常染色质臂内大约10 - 15个位点以及染色中心。发现宿主DNA序列TANA在游牧元件的两侧被重复，并且似乎是游牧元件插入的优先靶位点。对已知具有靶位点偏好的逆转录转座子的pol基因产物中的锌指基序进行分析，表明整合酶亚基参与了那些显示插入位点特异性的逆转录转座子的靶位点选择。对几种已知逆转录转座子的类pol基因的预测氨基酸序列进行了比较，并确定了游牧元件与其他逆转录病毒样移动元件之间的系统发育关系。从这种概念性蛋白质分析以及对其结构特征的分析可以清楚地看出，吉普赛类逆转录转座子通常可以分为两个不同组中的一组。还讨论了这些组的系统发育关系。
