Retrotransposon gtwin: structural analysis and distribution in drosophila strains

Abstract

A search for noncanonical variants of the gypsy retrotransposon ( MDG4 ) in the genome of the Drosophila melanogaster strain G32 led to the cloning of four copies of the poorly studied 7411-bp gtwin element. Sequence analysis showed that gtwin belongs to a family of endogeneous retroviruses, which are widespread in the Drosophila genome and have recently been termed insect erantiviruses. The gtwin retrotransposon is evolutionarily closest to MDG4, as evident from a good alignment of their nucleotide sequences including ORF2 (the pol gene) and ORF3 (the env gene), as well as the amino acid sequences of their protein products. These regions showed more than 75% homology. The distribution of gtwin was studied in several strains of the genus Drosophila. While strain G32 contained more than 20 copies of the element, ten other D. melanogaster strains carried gtwin in two to six copies per genome. The gtwin element was not detected in D. hydei or D. virilis. Comparison of the cloned gtwin sequences with the gtwin sequence available from the D. melanogaster genome database showed that the two variants of the mobile element differ by the presence or absence of a stop codon in the central region of ORF3. Its absence from the gtwin copies cloned from the strain G32 may indicate an association between the functional state of ORF3 and amplification of the element. MOLECULAR GENETICS

Evolutionary pattern of the gtwin retrotransposon in the Drosophila melanogaster subgroup

“…The gtwin element is most closely related to the D. melanogaster gypsy endogenous retrovirus (Bowen and McDonald 2001). The gag, pol and env genes show, respectively, 53%, 76% and 77% of amino acid identity between gtwin and gypsy (Kotnova et al 2005).…”

Polymorphism of canonical and noncanonical gypsy sequences in different species of Drosophila melanogaster subgroup: possible evolutionary relations

“…Therefore, it seems that retrotransposons are unable to evade cellular control. However, as demonstrated, in some strains retrotransposons do escape cellular control and cause genetic instability, e.g., gypsy in Xam ¡ (one of the loci controlling transposon activity) MS (Lyubomirskaya et al 1990) and MG (Prud'homme et al 1995), and gypsy-like element gtwin in G32 (Kotnova et al 2005).…”

“…In addition, the G32 strain contains an increased number of gtwin copies (Kotnova et al 2005) and two large inversions in the 3rd chromosome, supposedly caused by recombination between gtwin elements (Stefanov et al 2007). Our in situ hybridization investigation of some other mobile elements shows that LINE-like elements Doc and Jockey are transposing in this strain (unpublished data).…”

Amplification of “defective” retrotransposon gtwin in D. melanogaster strain carrying large complex chromosomal aberration

“…2), and the other one (group A in Fig. 2) that was isolated from G32 D. melanogaster strain (Kotnova et al 2005). These two variants have a number of single nucleotide differences, two of which affect tRNA-primer binding site of the element that might impair retrotransposition.…”

“…Retrotransposon gtwin is the closest relative of gypsy endogenous retrovirus. It was discovered previously in silico (Bowen and McDonald 2001) and isolated later from G32 (Kotnova et al 2005).…”