The crystal structure was solved to 3.0 Å resolution in 2000, as shown in the figure in the reference.  In (A), notice that the separate subunits appear to be anchored through interactions between an alpha helix and an adjacent subunit.  In (B), there are six sets of three loops.  The red loop, known as loop II, contains three lysine residues and is thought to be involved in binding the ssDNA that is fed through the center of the enzyme.