Preparation of spin-labeled poly(U) and its activity in assays with eukaryotic ribosomes

ESR studies on the interaction of spin-labeled polynucleotides with ribosomes require a sufficient label-to-nucleotide ratio. Using three different spin labels (SL) we have elaborated a technique to label poly(U) up to a ratio of 1 SL per 30 uridine residues. This ratio is much higher than maximal values obtained by other authors. The SL-poly(U) was shown to have the same activity as unlabeled poly(U) to direct synthesis of poly(Phe). SL-poly(U) binds to rat liver ribosomes in the presence of Mg2+ as shown by ESR. Titration with EDTA leads to a release of SL-poly(U) from ribosomes.