Figure 1.

Structure of R1Bm element and its target site. (a) The genome organization of R1Bm is indicated; the ORFs are shown as boxes, and the positions of the EN and RT domains in ORF2 are indicated. tsd is shown as bold lines (top) or nucleotide sequence (shaded box, middle) in target plasmid pB109. (b) The sequence of the R1Bm EN domain expressed is indicated, with the putative active site residues mutagenized to alanine codons shaded. The expressed protein contained 43 amino acids derived from the pET15b vector at the C terminus, including 6 His residues (the remainder are designated X₃₃).