LINEs Mobilize SINEs in the Eel through a Shared 3′ Sequence

Abstract

We characterized members of the LINE (UnaL2) and SINE (UnaSINE1) families from the eel genome and found that these LINE/SINE partners share similar 3' tails. A retrotransposition assay in HeLa cells demonstrated that the 3' conserved tail of UnaL2 is necessary for its retrotransposition. This 3' tail is recognized in trans by the UnaL2 reverse transcriptase at a surprisingly high rate, and that of UnaSINE1 can also be recognized, thus providing experimental evidence that a SINE can be mobilized by the retrotransposition machinery of a partner LINE. We also demonstrated that short repeats at the 3' end of UnaL2 are required for retrotransposition suggesting that UnaL2 retrotransposes in a manner reminiscent of the reverse transcriptase activity of telomerases.

Origin and evolution of SINEs in eukaryotic genomes

“…By the presence of these signals, SINEs are divided into T þ and T À classes. The tail synthesis in other SINEs is thought to be mediated by the template translocation mechanism similar to that in telomerase (Kajikawa and Okada, 2002;Roy-Engel et al, 2005).…”

“…In contrast to all other TEs transcribed by RNA polymerase II, SINEs are transcribed by RNA polymerase III (pol III) and contain a pol III promoter in their sequence. SINEs encode no proteins and have to use LINE RT for their retrotransposition (Jurka, 1997;Kajikawa and Okada, 2002;Dewannieux et al, 2003). The transcribed SINE RNA binds to the LINE RT, which is followed by the reverse transcription and integration of a SINE copy into a new genomic location in a way described above for LINEs.…”

Repetitive sequence environment distinguishes housekeeping genes

“…The non-LTR retrotransposons consist primarily of the Long Interspersed Nuclear Element-1 (LINE-1, 15.6%) and the nonautonomous Alu element (10.1%). LINE-1 transposons encode the enzymatic activities required for both their own mobility and for the mobilization of Alu elements (Hagan and Rudin, 2002;Kajikawa and Okada, 2002;Dewannieux et al, 2003). Alu transposons differ from other SINEs in that they are not derived from tRNA genes, but rather from the 7SL RNA gene (Ullu and Tschudi, 1984;Quentin, 1994;Smit, 1996;Okada and Hamada, 1997;Terai et al, 1998;Lander et al, 2001) which encodes the RNA component of the signal recognition particle that mediates the translocation of nascent secretory and membrane proteins (Wild et al, 2004).…”

Recombinant SINEs are formed at high frequency during induced retrotransposition in vivo

“…Retrotransposition-competent cell lines have greatly assisted in understanding the mechanism of non-LTR retrotransposition in vivo [6][7][8][9][10] . Here we report the first such system in a parasitic protist E. histolytica.…”