1 H‐NMR studies on the gene‐5‐encoded single‐stranded DNA binding protein of the filamentous bacteriophage IKe

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Abstract
Under physiological conditions and at concentrations needed for NMR studies, severe aggregation of the gene‐5 protein of the filamentous phage IKe occurs. Conditions are described for which well‐resolved 1H‐NMR spectra of the protein can be obtained. The aromatic part of the spectrum is analyzed by means of two‐dimensional NMR techniques; a complete interpretation is presented. Oligonucleotide binding studies reveal that just one phenylalanyl residue and one tyrosyl residue are influenced by the binding of rAMP, (dA)2, (dA)3, (dA)4, (dA)6, d(pT)3 or (dT)4. Upon binding, the aromatic resonances of these amino acid residues are shifted upfield by about 0.4–0.5 ppm. NMR measurements at different pH values demonstrate that only one of the two histidyl residues is freely titratable. From CIDNP experiments it is concluded that three out of five tyrosyl residues are located at the surface of the protein. Measurements carried out as a function of protein concentration indicate the occurrence of specific protein‐protein interactions between dimeric gene‐5‐protein molecules. The data obtained are compared with those available for the gene‐5 protein of M13. It follows from the comparison that these proteins mimic each other in almost every respect.