Vaury C, Pélisson A, Abad P, Bucheton A
Laboratoire de Biochimie Médicale, Université d'Auvergne, Clermont-Ferrand, France.
Genet Res. 1993 Apr;61(2):81-90. doi: 10.1017/s0016672300031177.
I factors are transposable elements of Drosophila melanogaster similar to mammalian LINEs, that transpose by reverse transcription of an RNA intermediate and are responsible for the I-R system of hybrid dysgenesis. There are two categories of strains in this species: inducer, that contain about 15 I elements at the various sites on chromosomal arms, and reactive, that lack active I factors. I elements occur in various Drosophila species. Potentially functional I factors from Drosophila teissieri can transpose when introduced by P-element-mediated transformation in a reactive strain of Drosophila melanogaster. We have studied the properties of Drosophila melanogaster strains into which such an I factor from Drosophila teissieri, named Itei, was introduced. Typical hybrid dysgenesis is produced when males carrying Itei are crossed with reactive females. However, more than one copy of the element seems necessary to produce dysgenic traits, whereas only one I factor of Drosophila melanogaster seems to be sufficient. The copy number of Itei in transformed lines maintained by endogamous crosses increases rapidly and stabilizes at values similar to those observed in inducer strains. As Drosophila teissieri contains much fewer copies than the Drosophila melanogaster strains, this suggests that the copy number of I elements is not simply regulated by sequences present in the element itself.
I因子是黑腹果蝇的转座元件，类似于哺乳动物的长散在核元件（LINEs），通过RNA中间体的逆转录进行转座，并导致杂种不育的I-R系统。该物种有两类菌株：诱导型，在染色体臂的不同位点含有约15个I因子；反应型，缺乏活性I因子。I因子存在于多种果蝇物种中。当通过P因子介导的转化将来自蒂氏果蝇的潜在功能性I因子引入黑腹果蝇的反应型菌株时，它们可以转座。我们研究了引入来自蒂氏果蝇的这种I因子（命名为Itei）的黑腹果蝇菌株的特性。携带Itei的雄性与反应型雌性交配时会产生典型的杂种不育。然而，似乎需要不止一个该元件的拷贝才能产生不育性状，而黑腹果蝇的一个I因子似乎就足够了。通过近亲杂交维持的转化系中Itei的拷贝数迅速增加，并稳定在与诱导型菌株中观察到的值相似的水平。由于蒂氏果蝇含有的拷贝数比黑腹果蝇菌株少得多，这表明I因子的拷贝数并非简单地由元件本身存在的序列调控。
