Intrinsic viscosities of cyclic and linear λ DNA

The ratio of the intrinsic viscosities of the linear and circular forms of λ DNA, [η] L /[η]c, has been measured as a function of ionic strength in the range [Na + ] = 0.6. M –0.03 M Corrections were made for the presence of uncyclizable linear contaminant in circular preparations. By combining data in the literature on the ionic strength dependence of linear DNA of various molecular weights with that obtained here, it was possible to determine the expansion parameter ε L as a function of [Na + ]. ε L is defined by the relation 〈L 2 〉 = b 2 N 1+εL , where 〈L 1 〉 is the mean‐square end‐to‐end distance of a chain of N segments of length b . The empirical relation ε L = 0.05 − 0.11 log [Na + ] for native NaDNA at 25°C is found. When ε L = 0, [η] L /[η]c extrapolates to 1.6, in good agreement with the theoretical prediction of 1.55. As ε L increases, [η] L /[η]c increases, in agreement with a theory of Bloomfield and Zimm.