Structural insights into translational recoding by frameshift suppressor tRNA^SufJ

Conformation of ASL^SufJ in the 70S A site. (A) ASL^SufJ (blue) forms three Watson–Crick base pairs with three nucleotides of the ACC-A codon (green) in the zero frame (no paromomycin). Although the C31.5 insertion (red) increases the anticodon loop to eight nucleotides, the ASL is recognized as cognate with 23S rRNA nucleotide A1913 (tan) maintaining a hydrogen bond interaction with the 2′-OH of A37. (B) Overlay of ASL^SufJ and ASL^Thr (gray) bound in the 70S A site shows the C31.5 insertion displaces the 5′ and 3′ phosphate backbone by 4 Å and 7 Å, respectively. This narrowing of the major and minor grooves of ASL^SufJ also results in the entire stem tilting 11.5° toward the back of the A-site decoding center. (C) Secondary structure representation of ASL^Thr and ASL^SufJ shows that the 31.5 insertion changes the conserved interaction between the U32·A38 (green) to C31.5 (red)·A38. The nucleotides that are gripped by 16S rRNA residues G1338 and A1339 upon translocation to the P site are highlighted in gray.