co nd - m at / 9 90 93 67 25 S ep 1 99 9 Twist Memory in Single - and Double - Stranded Polymers

We demonstrate a variant of the Bond Fluctuation lattice Monte Carlo model which conserves a topological linking number by forbidding moves through cis conformations. Unlike previous models that conserve linking number, our simulated ring chains have flexibility and the scaling properties of a lattice self-avoiding walk. Increased linking number reduces the radius of gyration mildly. A linking number of order 0.2 per bond leads to an eight-percent reduction of the radius for 128-bond chains. This percentage appears to rise with increasing chain length, contrary to expectation. For ring chains evolving without the conservation of linking number, we demonstrate a substantial anti-correlation between the twist and writhe variables whose sum yields the linking number. We raise the possibility that our observed anti-correlations may have counterparts in the most important practical polymer that conserves linking number, DNA.