Binding of Spermine to tRNATyr Stabilizes the Conformation of the Anticodon Loop and Creates Strong Binding Sites for Divalent Cations

Abstract

ESR spectra of yeast tRNATyr, spin-labeled in the isopentenyladenosine residue adjacent to the anticodon, were measured as a function of temperature at various spermine/tRNA ratios. The critical temperature, at which a change in the activation energy for spin-label motion takes place, changes abruptly by almost 10.degree. C upon the addition of the 5th spermine molecule/tRNATyr molecule, indicating a marked stabilization of the anticodon region. Scatchard plots for Mn2+ binding to tRNATyr in the presence of spermine do not follow theoretically predicted curves for electrostatic type of interaction, assuming that 4 negative charges on tRNA are neutralized by each spermine molecule. Two to three new binding sites for divalent cations are created upon the binding of spermine to tRNATyr.