AN APPROACH TO THE EVALUATION OF RNA SOLUTION STRUCTURE AND METAL COORDINATION CHEMISTRY BY TITRATION CALORIMETRY

Binding of divalent magnesium to RNA homopolymers was evaluated by tit ration calorimetry and analyzed in terms of the McGhee and von Hippel model of a one-dimensional infinite lattice. Examination of Mg2+ bindi ng data for ds poly(A) x poly(U), ss poly(A), and ss poly(U) revealed that the sign of the enthalpy term relates to the mode of metal bindin g (inner or outer sphere), which in turn is directly related to the st ructural ordering of the polynucleotide in solution. This approach pro vides details of the thermodynamics of metal binding, stoichiometry, a nd coordination chemistry that underlie the structural and catalytic c hemistry of RNA and offers a potential new probe of the solution struc ture of nucleic acids.