Electric dichroism of deoxyribonucleic acid in aqueous solutions: electric field dependence

The ionic strength and molecular weight dependence of the electric field dichroism of DNA, using native and sonicated calf thymus DNA, has been examined in the range of 0.09-1.0 mM NaCl solutions for molecular weights ranging from 1.24 x 10(5) to 44 x 10(5). The application of a classical theoretical analysis implies that the orientation results from an induced moment which appears to saturate at moderate fields of several killivolts per centimeter and that the induced moment is at least partly characteristic of that expected of a polyion whose charge is partially counterion compensated. The orientation leads to dichroism values which are in accord with other observations and are lower than expected for a B-form rod of DNA. These values, however, are not uniquely interpretable as resulting from base tilting.