Double-resonance experiments at 500 MHz on gene-5 protein and its complex with octadeoxyriboadenylic acid.

In this paper, a detailed description is presented of the aromatic part of the 500-MHZ 1H nuclear magnetic resonance (NMR) spectrum of the helix-destabilizing gene-5 protein (GVP) encoded by the coliphage M13. As a result of the resolution obtained at 500 MHZ, it was possible to perform selective decoupling and time-resolved selective Overhauser experiments. The magnitudes of the observed Overhauser effects compare favorably with magnitudes expected on the basis of theoretical calculations. These experiments in conjunction with selective decoupling experiments allowed a detailed interpretation of the aromatic part of the protein spectrum. The spectrum of the aromatic part of the GVP-d(A)8 complex could be interpreted in a similar fashion. The ring protons of one phenylalanyl residue and of two tyrosyl residues show rather large shifts upon complex formation. This indicates that these residues are involved in the interaction with the DNA molecule in accordance with earlier observations. Direct evidence for the proximity of these aromatic rings and the DNA fragment in the complex was obtained by additional Overhauser experiments. It turns out that the H3',H4', and/or the H5' sugar protons of the oligonucleotide are situated near the ring protons of (most likely) two or all three of the aromatic residues of which the resonances undergo large shifts upon complex formation.