(
2009-08)
Gladyshev, Eugene A.; Arkhipova, Irina R.
Ribosomal DNA genes in many eukaryotes contain insertions of non-LTR
retrotransposable elements belonging to the R2 clade. These elements persist in
the host genomes by inserting site-specifically into multicopy target sites, thereby
avoiding random disruption of single-copy host genes. Here we describe R9
retrotransposons from the R2 clade in the 28S RNA genes of bdelloid rotifers,
small freshwater invertebrate animals best known for their long-term asexuality
and for their ability to survive repeated cycles of desiccation and rehydration.
While the structural organization of R9 elements is highly similar to that of other
members of the R2 clade, they are characterized by two distinct features: sitespecific
insertion into a previously unreported target sequence within the 28S
gene, and an unusually long target site duplication of 126 bp. We discuss the
implications of these findings in the context of bdelloid genome organization and
the mechanisms of target-primed reverse transcription.
