[Spatial structure of cro-repressor in a solution. II. Effect of ionized groups].

The technique of 1H NMR spectroscopy and absorption UV spectroscopy were used to study the ionization of the tyrosine phenol cycles and the effect of ionizable groups on the chemical shifts of signals from protons in the side chains of several amino acid residues. The microenvironment of these residues was established by analysing the titration curves. The mutual orientation of two functionally important adjacent alpha-helical protein regions was determined in solution. The signals from methionine residues belonging to different regions of the secondary structure were assigned in the NMR spectrum. The results indicate that the spatial structure of the repressor is similar in solution an in the crystal. They confirm the model proposed for the cro repressor interaction with DNA and based on the data of X-ray diffraction analysis.