The L11 P-site loop is largely comprised of polar amino acids and carries a net positive charge, making it ideal for interactions with the phosphate backbones of nucleic acids, e.g. rRNA and tRNA. Positioned between H84 and the peptidyl-tRNA T-loop, several of its amino acids are within H-bonding distance of H84 ($3.3 Å ), while C56 of the peptidyl tRNA T-loop comes within 2.1 Å of G58 in the L11 P-site loop (4, 5) , suggesting that the L11 P-site loop can directly interact with both of the RNA-based structures. While currently available X-ray crystal structures are unavailable for ratchet-state ribosomes, a recently published examination of tRNA movement through the E. coli ribosome using large-scale analysis of cryo-EM images implicates the P-site loop as a dynamic arm interacting with and moving in relation to tRNAs passing across the P-site (44) . Although these studies were performed at resolutions of 9-20 Å , leaving considerable ambiguity regarding the precise residues involved, they clearly reveal highly dynamic interactions between the P-site loop and both P-site, and E-site tRNAs.