Abstract
E. coli formylmethionyl tRNA (tRNA(fMet)) has been irradiated with ultraviolet light in the presence of Mg(2+) to the extent of 50 per cent inactivation of amino acid acceptance. Separation of active and inactive molecules after irradiation has shown that ultraviolet light modification of the uridine in the anticodon, the uridine in the small loop, the 4-thiouridine, and the pyrimidines in the double-stranded stem adjacent to the dihydrouridine loop has no effect on aminoacylation or transformylation. The ultraviolet light-induced inactivation of methionine acceptance by tRNA(fMet) is due almost entirely to modification of the cytidine residues in the 3'-terminal CCA-OH sequence.