Structure and function of Escherichia coli formylmethionine transfer RNA : II. Effect of modification of guanosine residues on aminoacyl synthetase recognition

Abstract

Guanosine residues in Escherichia coli formylmethionine transfer RNA have been modified by photo-oxidation in the presence of methylene blue. After irradiation to the extent of 50% loss of amino-acid acceptor activity, separation of active and inactive molecules has shown that guanosine rsesidues in the stem adjacent to the dihydrouridine loop and the guanosine at position no. 2 from the 5′ terminus are not required for aminoacylation or transformylation. Active molecules containing these modifications are amino-acylated with a K m threefold higher than that for unmodified tRNA fMet. No change in V max occurs. Modification of a guanosine residue in the small loop joining the anticodon stem and the TΨC stem results in inactivation of methionine acceptor activity. This represents the first experimental evidence that a modification in this region affects the aminoacylation of a tRNA.