Tangle Solutions for a Family of DNA-Rearranging Proteins
  We study two systems of tangle equations that arise when modeling the action of the Integrase family of proteins on DNA. These two systems--direct and inverted repeats--correspond to two different possibilities for the initial DNA sequence. We present one new class of solutions to the tangle equations. In the case of inverted repeats we prove that any solution not in these, or 2 previously known classes, would have to belong to one specific class. In the case of direct repeats we prove that the three classes are are the only solutions possible. 
Dorothy Buck and Cynthia Verjovsky Marcotte