The binding of an avian myeloblastosis virus basic 12,000 dalton protein to nucleic acids

The binding of a basic 12,000 dalton protein (p12) from avian myeloblastosis virus to viral RNA and heterologous DNA has been investigated. The binding stoichiometries and constants were determined by an extrinsic fluorescence assay. In both cases each bound p12 molecule occupies four nucleotides and the apparent binding constant is approximately 1 x 10(6) M-1. Binding is non-cooperative and there is no apparent difference in the interaction of p12 with viral RNA or heterologous single-strand DNA. The relative binding constant at various ionic strengths was assayed by the nitrocellulose filter procedure. Analysis of the data revealed that each bound p12 molecule forms three ion pairs with the nucleic acid.