We develop topological methods for analyzing difference topology experiments
involving 3–string tangles. Difference topology is a novel technique used to unveil the
structure of stable protein-DNA complexes. We analyze such experiments for the Mu
protein-DNA complex. We characterize the solutions to the corresponding tangle
equations by certain knotted graphs. By investigating planarity conditions on these
graphs we show that there is a unique biologically relevant solution. That is, we show
there is a unique rational tangle solution, which is also the unique solution with small
crossing number.
Keywords
3–string tangle, DNA topology,
tangle method, difference topology, Mu transpososome, graph
planarity, Dehn surgery, handle addition lemma