Functional interaction between tRNA2Gly2 at the ribosomal P-site and RF1 during termination at UAG

The glycine codons GGA or GGG, on the 5' side of stop codons UAG and UGA, are associated with a uniquely low termination efficiency in Escherichia coli, as compared to other codons, including the two glycine codons GGU and GGC. In contrast to the wild-type strain, all four glycine codons have a similar effect on termination at UAG in a strain with a mutant release factor 1 (RF1). Thus, these two glycine codon pairs, when present at the ribosomal P-site, affect termination efficiency of mutant or wild-type RF1 at UAG differently. If reading of GGA/G by tRNAGly2 is eliminated in the RF1 wild-type strain and replaced by a mutant form of tRNAGly3, termination efficiency is increased to the same level as for GGU/C, normally read by tRNAGly3. The results suggest an unusual interaction between the P-site tRNAGly2 and wild-type RF1 at the ribosomal A-site that is not present with mutant RF1.