Characteristics of retrotransposition Activity of the gtwin retrovirus of the Drosophila melanogaster line G32

42 Mobile genetic elements account for a considerable part of eukaryotic genome and significantly affect its stability. They are involved in mutagenesis, regulation of gene expression, and occurrence of genomic rearrangements. In view of this, the study of the mechanisms by which the activity of transposable elements is regulated by cellular factors is of great interest. For this purpose, it is convenient to use model objects in the genome of which mobile genetic elements are transposed and amplified. The behavior of mobile genetic elements in different Drosophila species has been described sufficiently well so far. There are many Drosophila strains characterized by genetic instability caused by amplification and transposition of mobile genetic elements. In such strains, an increased frequency of mutations and reversions as well as occurrence of chromosomal rearrangements is observed. A characteristic feature of D. melanogaster laboratory strain G32 is unusual behavior of some mobile elements. In particular, this strain characterized by substantial amplification of the gtwin retrotransposon, which is closely related to gypsy , one of the most comprehensively studied mobile genetic elements. Evidences indicating that currently gtwin undergoes transpositions have not been obtained [1]. In addition, we detected a large chromosomal aberration in this linea with an increased number of sites where gtwin and some other mobile genetic elements are located [2]. It is known from published data that mobile genetic elements are inhomogeneously distributed over the genome, which leads to occurrence of clusters playing a major role in the regulation of transposition activity [3]. Taking into account this information and the fact that the number of gtwin copies in the G32 strain was approximately 30 (which is one order of magnitude larger than the commonly detected number of copies of this element), we assumed that different gtwin copies may be located in the immediate vicinity of one another. In this study, we tested a series of D. melanogaster strains for the presence of neighboring gtwin copies by PCR using genomic DNA as a template. The annealing sites for PCR primers were located at both ends of gtwin in the vicinity of its long terminal repeats (LTRs). Synthesis proceeded in the direction of the genomic environment of the element.