Figure 1. Crystal structure of the PFV STC.

a, Sequence of the model tDNA. The arrows point to the sites of strand transfer with a 4-bp stagger (boxed). Nucleotide numbers are indicated for both strands. The green diamond indicates the 2-fold symmetry axis. b-c, Surface (b) and cartoon (c) representations of the STC crystal structure, viewed along or perpendicular to the crystallographic two-fold axis, respectively. IN active site carboxylates are shown in red. Protein domains (NTD, N-terminal domain; CTD, C-terminal domain; CCD, catalytic core domain; NED, NTD extension domain) as well as viral (v) and target (t) DNAs are indicated.