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

Electron spin resonance (ESR) spectra of yeast tRNATyr, spin‐labelled 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°C upon the addition of the fifth 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 four negative charges on tRNA are neutralized by each spermine molecule. It was estimated that two to three new binding sites for divalent canons are created upon the binding of spermine to tRNATyr.