Increasing viscosity of E. coli chromatin with increasing shear

We have observed that the viscosity of a solution of E. coli chromatin increases as the shear to which the solution is subjected is suddenly increased. This dilatant effect is opposite to the usual thixotropic non-Newtonian effects that are observed in DNA solutions. We suggest that the observed dilatancy may be explained in terms of shear-induced aggregation of large DNA molecules. Conditions for aggregation are discussed in the context of the “cluster theory” of condensation.