Ultraviolet inactivation of the functions of phenylalanine and lysine transfer RNA's of Escherichia coli

Abstract

Ultraviolet inactivation of phenylalanine and lysine transfer RNA's (tRNA Phe and tRNA Lys) of Escherichia coli was studied with respect to amino acid acceptance, amino acid transfer to ribosomes, and specific binding to 70-S ribosomes and 30-S ribosomal subunits. It was found that the cross sections of the specific binding to 70-S ribosomes and to 30-S subunits were identical to each other for both tRNA Phe and tRNA Lys. The cross section of the amino acid transfer to ribosomes was also almost identical to that of the specific binding for both of the tRNA's. In the case of tRNA Phe, the cross section of amino acid transfer to ribosomes from tRNA irradiated in the deacylated state was nearly equal to the sum of the cross section of the aminoacylation and that of the transfer from the tRNA irradiated in the aminoacylated state, indicating nonoverlapping of the functional sites responsible for amino acid acceptance and transfer. On the other hand, a substantial overlap of the critical sites for the two functions was indicated for tRNA Lys. When the tRNA's were irradiated in the solution with Mg 2+, the inactivation cross sections decreased compared to those obtained by irradiation in the solution without Mg 2+ and with low salt content, but the above interrelationship between the cross sections remained essentially the same for both sets of irradiation conditions.