Structure of a typical full-length human L1 element. The 5′ untranslated region (UTR) has a regulatory function; open reading frame 1 (ORF I) encodes an RNA-binding protein; ORF II encodes the L1 replicase and contains an endonuclease (EN) and a reverse transcriptase domain (RT), and the 3′ UTR that contains a conserved G-rich polypurine motif. Genomic copies of L1 usually end in an A-rich stretch (open rectangle, see Moran and Gilbert 2002). The partial alignment of Ta-1, Ta-0, L1PA2, and L1PA5 consensus sequences shows the positions of oligonucleotide 1, which is specific for Ta-1, and of oligonucleotide 2, which includes the ACA trinucleotide, diagnostic of the Ta family (see Methods). The numbers indicate the position of the sequence on alignment ALIGN-000165 at the EMBL_ALIGN database (Boissinot and Furano 2001).
