Integration of DNA copies in a host genome is a necessary stage in the life 
cycle of retroviruses and LTR-retrotransposons. There is still no clear 
understanding of integration specificity of retroelements into a target site. 
The selection of the target DNA is believed to potentially affect a number of 
factors such as transcriptional status, association with histones and other 
DNA-binding proteins, and DNA bending. The authors performed a comprehensive 
computer analysis of the integration specificity of Drosophila melanogaster 
LTR-retrotransposons and retroviruses including an analysis of the nucleotide 
composition of targets, terminal sequences of LTRs, and integrase sequences. A 
classification of LTR-retrotransposons based on the integration specificity was 
developed. All the LTR-retrotransposons of the gypsy group with three open 
frames (errantiviruses) and their derivatives with two open frames demonstrate 
strict specificity to a target DNA selection. Such specificity correlates with 
the structural features of the target DNA: bendability, A-philicity, or 
protein-induced deformability. The remaining LTR-retrotransposons (copia and BEL 
groups, blastopia and 412 subgroups of the gypsy group) do not show specificity 
of integration. Chromodomain is present in the integrase structures of blastopia 
and 412 subgroup LTR-retrotransposons and may facilitate the process of 
non-specific integration.