Characterisation of a new, fully active fluorescent derivative of E. coli tRNA Phe

E. coli tRNAPhe has been labelled with fluorescein isothiocyanate taking advantage of the reactivity of this compound for primary aliphatic amino groups as exist in this tRNA as the modified base X(3-(3-amino-3-carboxypropyl)uracil). The extent of labelling was calculated as 1.6 nmole/A260 unit suggesting one dye molecule per tRNA. The FITC-tRNA showed full activity in aminoacylation and polypeptide synthesis. The absorption and fluorescence of the label respond markedly on addition of Mg++ to the tRNA. The label appears to be a sensitive probe of tRNAPhe tertiary structure.