Fig. 5. Two-dimensional gel analysis of HJs formed by recombination between psi and psiDC sites. (A) Analysis of products formed by recombination on p-psiDC.psi. (B) Analysis of products formed by recombination on p-psiDC.psiDC. The first dimension separated substrates and products according to their topology, and the second dimension separated products according to their restriction pattern. Arrows indicate the positions of HJ intermediates on each gel. Migration of three-noded knots, four-noded catenanes and other species in the first dimension is indicated to the left of a duplicate first- dimension lane as in the legend to Figure 2. Second-dimension mobilities are shown above the gels as HJ, HJ intermediates; L, linear substrate; S, substrate restriction fragment; and P, product restriction fragment. Small product and substrate restriction fragments are not shown. Partial digestion with XhoI gave some linear substrate at the oc S position, and some uncut (open circle) large product circle at the four-node position in (B).