Mobile dispersed genetic element MDG1 of Drosophila melanogaster: nucleotide sequence of long terminal repeats

Abstract

Long terminal repeats (LTRs) of two members of mdg1 family were sequenced. In the both cases, they are represented by perfect direct repeats 442 and 444 bp in length. Sixteen nucleotides in the LTRs of two different mdg1 elements are different. Each LTR contains slightly mismatched 16-nucleotide inverted repeats located at the ends of the LTR. Six base pairs closest to the termini of LTR form perfect inverted repeats. On the gene-distal sides of LTRs, short 4-nucleotide direct repeats are located, probably representing the duplication of a target DNA sequence arising from insertion of mdg. They are different in the two cases analyzed. Just as the other analyzed eukaryotic transposable elements, mdg1 starts with TGT and ends with ACA. Within the both strands of LTR, the sequences similar to Hogness box (a putative signal for RNA initiation, or a selector) and AATAAA blocks (putative polyadenylation signals) are present. The LTR of mdg1 contains many short direct and inverted repetitive sequences. These include a 10-nucleotide sequence forming a perfect direct repeat with the first ten nucleotides of the LTR. A region of LTR about 70 bp long is represented by simple repetitive sequences (TAT).

A Brief History of the Status of Transposable Elements: From Junk DNA to Major Players in Evolution

“…Several Russian teams were in the vanguard of this research, and they referred to the first TEs of Drosophila as ''mobile dispersed genes'' (mdg), a term that everybody could understand. mdg1, mdg2, mdg3, and mdg4 were the first to be discovered and described (Ananiev and Ilyin 1981;Kulguskin et al 1981;Gvozdev et al 1981). This numerical nomenclature was soon superseded by more colorful names such as gypsy (mdg4), copia, and 412.…”

Variability, Recombination, and Mosaic Evolution of the Barley BARE-1 Retrotransposon

“…Although LTRs are the most rapidly evolving region of the LTR retrotransposons (Kulguskin et al 1981;Lankenau et al 1990;Lyubomirskaya et al 1990;Mizrokhi and Mazo 1990), they also contain some functionally important regions: the terminal segments, recognized by integrase, the promoter and enhancer elements, and the RNA processing signals. The data here show that the termini of BARE LTRs are conserved.…”

Evolution of the copia retrotransposon in the Drosophila melanogaster species subgroup

“…This selective constraint could maintain high levels of sequence homology among copia elements from diverged species. However, similar control sequences are present in other LTR retrotransposons which do not show similar high levels of interspecific sequence homology (Kulguskin, Ilyin, and Georgiev 1981;Lankenau et al 1990;Lyubomirskaya et al 1990;Mizrokhi and Mazo 1991).…”

“…A priori, it seems unlikely that the noncoding copia LTR-ULR region could be evolving so slowly as to account for this low level of divergence. Previous studies which have looked at sequence evolution in the same region of various retrotransposon families have found much higher levels of divergence between elements of a particular family both within and between species (Kulguskin, Ilyin, and Georgiev 1981;Lankenau et al 1990;Lyubomirskaya et al 1990;Mizrokhi and Mazo 1991).…”