[Electrostatic interaction and differences in specific and nonspecific interactions of the Lac-repressor with DNA]

To investigate the complexes of lac-repressor with specific and non-specific DNA sequences method of covalent cross-linking of proteins to partially depurinated DNA was used. We have identified the amino acid resides which form cross-links and hence are proximate to DNA. Only lysine 33 is cross-linkable in specific complex. In the case of non-specific complex (at the presents of inducer molecules) lysine 33 remains cross-linkable. Some consequences of these phenomena in aspects of the physical backgrounds of protein-DNA interactions have been discussed.