L1-mediated retrotransposition of murine B1 and B2 SINEs recapitulated in cultured cells.
SINEs are short interspersed nucleotide elements with transpositional activity, present at a high copy number (up to a million) in mammalian genomes. They are 80-400 bp long, non-coding sequences which derive either from the 7SL RNA (e.g. human Alus, murine B1s) or tRNA (e.g. murine B2s) polymerase III-driven genes. We have previously demonstrated that Alus very efficiently divert the enzymatic machinery of the autonomous L1 LINE (long interspersed nucleotide element) retrotransposons to transpose at a high rate. Here we show, using an ex vivo assay for transposition, that both B1 and B2 SINEs can be mobilized by murine LINEs, with the hallmarks of a bona fide retrotransposition process, including target site duplications of varying lengths and integrations into A-rich sequences. Despite different phylogenetic origins, transposition of the tRNA-derived B2 sequences is as efficient as that of the human Alus, whereas that of B1s is 20-100-fold lower despite a similar high copy number of these elements in the mouse genome. We provide evidence, via an appropriate nucleotide substitution within the B1 sequence in a domain essential for its intracellular targeting, that the current B1 SINEs are not optimal for transposition, a feature most probably selected for the host sake in the course of evolution.
Dewannieux
Marie
M
Unité des Rétrovirus Endogènes et Eléments Rétroïdes des Eucaryotes Supérieurs, UMR 8122 CNRS, Institut Gustave Roussy, 39 rue Camille Desmoulins, 94805 Villejuif Cedex, France.
Heidmann
Thierry
T
D000818:Animals; D001483:Base Sequence; D004251:DNA Transposable Elements / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D020084:Long Interspersed Nucleotide Elements / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D010802:Phylogeny; D020733:RNA, Small Cytoplasmic / Q000235:genetics*; D012343:RNA, Transfer / Q000235:genetics*; D011995:Recombination, Genetic / Q000235:genetics; D020086:Short Interspersed Nucleotide Elements / Q000235:genetics*; D018271:Signal Recognition Particle / Q000235:genetics*
C115990:7SL RNA; D004251:DNA Transposable Elements; D020733:RNA, Small Cytoplasmic; D018271:Signal Recognition Particle; C503637:Srp72 protein, mouse; D012343:RNA, Transfer