Ribonucleic acid codons and protein synthesis: XIII. RNA codon recognition by deacylated tRNA and aminoacyl-tRNA

Abstract

The attachment of deacylated tRNA and [ 14C]Phe-tRNA to ribosomes in response to poly U was studied. The extent of binding of tRNA Phe to ribosomes is approximately equal to that of [ 14C]Phe-tRNA. Transfer RNA dilutes the binding of [ 14C]Phe-tRNA as predicted from the ratio of tRNA to aminoacyl-tRNA, suggesting that tRNA Phe and [ 14C]Phe-tRNA have approximately equal affinities for ribosomal binding sites. Under the conditions studied, tRNA and [ 14C]Phe-tRNA are released from poly U-ribosome complexes at relatively slow rates. The synthesis of phenylalanyl-puromycin peptides was detected at 0.02, but not 0.01 m-Mg 2+. At 0.01 m-Mg 2+, tRNA inhibits AUG-dependent binding of N-formyl-[ 3H]Met-tRNA to ribosomes and the formation of N-formyl-[ 3H]methionyl uromycin. These data show that the rate of codon recognition of initiator and other codons by aminoacyl-tRNA at two or more ribosomal sites may be affected by the ratio of tRNA to aminoacyl-tRNA.