Mechanism of enhancement of polynucleotide binding to cells by mutagens.

The binding of polyuridylate to cells is substantially increased by proflavine. This enhanced binding is saturable with respect to time and to the concentration of both proflavine and polyuridylate. Enhancement is observed only when cells are exposed to both proflavine and polyuridylate together and depends cooperatively on the proflavine concentration. The resulting complex formed between the cell, proflavine, and polyuridylate can be dissociated with salt but not with sucrose solutions. An increase in the binding of polyuridylate to cells similar to that observed with proflavine was also obtained with cationic dyes such as acridine orange, 9-aminoacridine, and Hoechst 33258, while the introduction of a bulky polysaccharide residue, dextran, into the dyes cancels these effects. Similarly, cationic aromatic compounds such as primaquine and quinacrine which carry bulky nonplanar substituents or aliphatic cationic compounds like ethylenediamine do not enhance binding. Proflavine is unable to augment the binding of a basic macromolecule, diethylaminoethylaminoethyldextran, to cells. The model proposed for the enhanced binding of polyuridylate is based on the cooperative formation of stacked complexes of cationic dye located between the cell surface and the bound polyuridylate.