Insertions in the anticodon loop of tRNA1Gln(sufG) and tRNA(Lys) promote quadruplet decoding of CAAA

Base insertion mutations in the anticodons of two different Escherichia coli tRNAs have been isolated that allow suppression of a series of +1 frameshift mutations. Insertion of a U between positions 34 and 35 of tRNAGln1 or addition of a G between positions 36 and 37 of tRNA(Lys) expand the anticodons of both tRNAs similarly to 3'-GUUU(-5') and allow decoding of complementary 5'-CAAA(-3') quadruplets. Analysis of the suppressed mRNA sequences suggests that suppression occurs by pairing of the expanded anticodons to all four bases of the complementary, quadruplet codon. The tRNA Gln mutants are identical to the sufG class of frameshift suppressors isolated both in Salmonella enterica serovar Typhimurium and E. coli by Kohno and Roth and previously thought to affect tRNA(Lys).