Base specificity of polyamine binding to synthetic polynucleotides

The binding of polyamines and magnesium to synthetic polynucleotides has been studied by gel filtration on a Sephadex G-50 column. Among the single-stranded polynucleotides examined [poly(A), poly(C), and poly(U)], polyamines were found to bind to poly(C) and poly(U) preferentially, while the binding of Mg2+ was greatest with poly(A). Spermine bound to poly(U) was displaced completely by NH4+ but incompletely by Mg2+, while Mg2+ bound to poly(A) was displaced completely be spermine but incompletely by NH4+. The optimal pH for the binding of spermine to poly(U) was found to be about 7.9, while Mg2+ could bind to poly(A) over a broad pH range (7.1--8.7).