Hagemann S, Miller W J, Haring E, Pinsker W
Institut für Medizinische Biologie, AG Allgemeine Genetik, Universität Wien, Vienna, Austria.
Chromosoma. 1998 Mar;107(1):6-16. doi: 10.1007/s004120050277.
A potentially full-sized P element isolated from the genome of Drosophila ambigua by polymerase chain reaction amplification was completely sequenced. It has a length of 3329 bp and the termini are formed by 33 bp inverted repeats. Sequence comparisons show that it can be classified as a member of the T-type P element subfamily. The translational reading frames of all four exons are interrupted by stop codons and frameshift mutations. At the 3' end of exon 3 a 687 bp insertion sequence (IS-amb-P) is found that also occurs in the form of dispersed copies (IS-amb) in the genome in D. ambigua. At the interspecific level it shows homology to mobile sequences of other species of the obscura group. Although variable in length, these IS elements are characterized by conserved sections without coding function and by 14 bp inverted repeats, one at a terminal, the other at a subterminal position. In situ hybridization revealed that P elements in D. ambigua are restricted to only two euchromatic sites on chromosome elements A and E. This situation resembles that found in Drosophila guanche and Drosophila subobscura where P homologs are clustered at a single site on chromosome element E and where the section corresponding to exon 3 of P elements carries an IS element. The gene sik-hom, which is located at the 5' side of the D. guanche cluster of P homologs, was used as a marker to examine whether the P element sites on chromosome element E of D. guanche and D. ambigua are homologous. The results suggest that the nested insertions of IS elements into P elements must have occurred independently in the two different lineages.
通过聚合酶链反应扩增从模糊果蝇基因组中分离出一个可能全长的P元件，并对其进行了全序列测定。它的长度为3329 bp，末端由33 bp的反向重复序列形成。序列比较表明，它可归类为T型P元件亚家族的成员。所有四个外显子的翻译阅读框都被终止密码子和移码突变打断。在外显子3的3'端发现了一个687 bp的插入序列（IS-amb-P），它在模糊果蝇基因组中也以分散拷贝（IS-amb）的形式出现。在种间水平上，它与暗果蝇组其他物种的可移动序列具有同源性。尽管这些IS元件长度可变，但其特征是具有无编码功能的保守区段和14 bp的反向重复序列，一个在末端，另一个在亚末端位置。原位杂交显示，模糊果蝇中的P元件仅局限于染色体元件A和E上的两个常染色质位点。这种情况类似于在加那利果蝇和次暗果蝇中发现的情况，其中P同源物聚集在染色体元件E上的单个位点，并且P元件外显子3对应的区段携带一个IS元件。位于加那利果蝇P同源物簇5'侧的sik-hom基因被用作标记，以检查加那利果蝇和模糊果蝇染色体元件E上的P元件位点是否同源。结果表明，IS元件嵌套插入P元件的情况一定是在两个不同的谱系中独立发生的。
