Specifity of DNA-basic polypeptide interactions. Influence of neutral residues incorporated into polylysine and...

An approach is described for evaluation of the specificity of basic polypeptides concerning the base pair composition of DNA. The polypeptides were covalently bound to CNBr activated agarose and two DNAs strongly different in base composition but of equal molecular weight were loaded and detached by a NaCl gradient. The difference in the NaCl concerntrations between the elution maxima of the two DNAs was taken as a measure for the recognition specificity. The results obtained confirmed the known AT- und GC-specificity of polylysine and polyarginine, respectively. Neutral residues incorporated into polylysine generally reduce the interaction affinity and also the AT-specificity of their host. This behavior is very pronounced with three homogeneous fractions of clupeine containing about one third of neutral aliphatic amino acids within clusters of arginine; the base pair specificity of these arginine copolymers was found to be practically nil.