Molecular phylogeny and systematics of drosophila retrotransposons and retroviruses

Full classification of Drosophila melanogaster retrotransposons with long terminal repeats (LTR-retrotransposons) has been recomposed, and their evolutional analysis in sequenced genomes of different species of drosophila and other arthropods has been carried out. D. melanogaster LTR-retrotransposons are divided in three groups: gypsy (one, two or three open reading frames - ORFs), copia (one ORF), BEL (one ORF). Gypsy group is divided into three subgroups. Subgroup I is underrepresented by retrotransposons-retroviruses with three ORFs and their derivatives which have lost the env gene (ORF3). Subgroup II is underrepresented by retrotransposons with two ORFs, subgroup III - by retrotransposons with one ORF. Comparative analysis of homologs of gypsy group LTR-retrotransposons evidences that subgroups I and II are only in genomes of Lepidoptera and Diptera. Gypsy group of LTR-retrotransposons with one and two ORFs are found in almost all genomes of arthropods. Most of the families of D. melanogaster gypsy group LTR-retrotransposons have close homologs in genomes of other species of drosophila. A degree of identity of retrotransposons sequences is correlated with a degree of relation between species of drosophila; it's evidences about vertical transmission of retrotransposons. Obvious cases of horizontal transfer of some mobile elements have been detected including retrotransposons without the env gene. Homologs of distinct ORFs of retrotransposons - genes gag and env - have been found. Gene-homolog of the gag gene - Grp (CG4680) - is under purifying selection; so it has an important function in drosophila genome.