A schematic representation of the template switch model for LTR-mediated retroposition. (VLP) virus-like particle; (RT) reverse transcriptase; (PR) protease; (IN) integrase. The black boxes in LTR retrotransposons correspond to the LTRs and the light green box to the ORF. The blue boxes correspond to exons encoded by the host genome and the white boxes to introns. The double template switch occurs in the VLP, generating a chimeric cDNA (multiple switches can occur) (Derr et al. 1991; Schacherer et al. 2004; Maxwell and Curcio 2007). After integration, the chimeric sequences can be transcribed as pseudo-LTR retrotransposons, which could be subject to further cycles of retroposition (Elrouby and Bureau 2010).
