Isolation and structural characterization of a CsRn1 -like element from the genome of Paragonimus westermani. (A) Schematic representation of an LTR retrotransposon contained in the genomic lambda clones (λPw-13-1 and λPw-13-2), which were homologous to the Pw-D-13 probe. Boxes with a filled arrowhead indicate a direct repeat sequence. The primer positions used in the retrieval of multiple copy sequences are also shown (INT-1, 5'-AGTTGGAAGCCACATTCGCGCTACG-3' and INT-2, 5'-GTGACAACAACCCTTCGATCCTGATG-3'). (B) Overall structure of the Paragonimus retrotransposon, named PwRn1. Gray box represents an open reading frame (ORF) encoding Gag, protease (PR), reverse transcriptase (RT), RNase H (RH) and integrase (IN). Duplicated target sites of 4 bp are indicated as target site duplication (TSD). The gag-pol boundary region was further verified by the nucleotide sequences of cDNA clones (see also the legend for Figure 6).