Figure 1.

Structure of a typical mammalian L1. Full-length elements are ~7 kb in length and have four major segments: 5′ and 3′ untranslated regions (UTRs) and two open reading frames (ORFs). ORF1 has a 5′ hypervariable region (V) and ORF2 contains four conserved domains: endonuclease (E), an octapeptide-containing sequence (Z), reverse transcriptase (RT) and a RNase-H-like zinc finger (C). A G-rich polypurine tract (G) resides in the 3′ UTR and elements terminate with a poly-A tail. The region cloned for this study straddles the RT domain in ORF2 and was isolated by PCR with degenerate primers.