Studies on DNA Unwinding

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Abstract
The interaction of gene V protein from bacteriophage M13 with the self-complementary tetranucleotide d(pC-G-C-G) was studied by 1H and 31P NMR. Using the H-bonded proton resonances of the Watson-Crick base pairs as a probe showed that the protein is able to unwind the small double-helical fragment even at 0.degree. C. Binding of the tetranucleotide causes changes in the aromatic part of the 1H NMR spectrum of the complex, suggesting that aromatic residues, most likely tyrosines, take part in the protein.cntdot.nucleic-acid interaction. From the 31P NMR spectra of the protein.cntdot.nucleic-acid complex it follows that the pK value of the 5''-terminal phosphate is lower than for the free nucleic acid species. The exchange of the protein between nucleic acid substrates is fast. Combination of these measurements indicated a mechanism of unwinding on the tetranucleotide level. To a large extent the unwinding is determined by fluctuations in the double-helical DNA structure.