Conversion of B DNA between solution and fiber conformations.

At low salt and high DNA concentration, rodlike DNA molecules form specific aggregates containing about seven parallel DNA molecules packed in a bundle. Bundle formation can be reversed by addition of small amounts of EDTA, and formation of the specific aggregates can be induced at higher salt concentration by addition of trivalent ions. In contrast to monomeric DNA, the aggregated species has the optical anisotropy expected for the B form as observed in fibers.