Abstract
1. Interactions of histone fractions with quinacrine mustard were investigated by fluorimetry and spectrophotometry and the results were interpreted with the aid of thinlayer chromatography. 2. Characteristic differences were found between the various histone fractions of calf thymus. The conditions that favoured histone conformational changes and aggregation, also favoured interaction between histones and the dye; low concentrations of SO(4) (2-) brought about more interaction than did Cl(-); urea, guanidinium and iodide ions were inhibitory to binding. 3. Changes in the physical state of all the quinacrine mustard-protein complexes occurred as a function of ionic strength and pH. The most salt-dependent interaction was found in the arginine-rich histone fraction. 4. The interaction of the calf thymus histone fractions with quinacrine mustard was compared with the interaction of bovine plasma albumin and protamine with quinacrine mustard. 5. The relationship between dye-binding and the aggregation of histone fractions was discussed.