During normal translation elongation, individual amino acids in the nascent chain (gray dots) do not make stable contacts with the ribosome exit tunnel (left diagram). By contrast, a subset of its amino acids in arrest peptides form interactions with the ribosome exit tunnel (red dots with dashed lines in the middle diagrams). These interactions typically form in the region of the exit tunnel between the PTC and a constriction site formed by uL22 and uL4. The interactions can distort the peptidyl-transferase center (PTC) or induce nascent chain secondary structure to alter the geometry of the peptidyl-tRNA. The consequence is an impairment of peptidyl transfer from the P-site tRNA (green) to the incoming aminoacyl-tRNA (orange). Arrest peptides can be released by factors that impart a pulling force, thereby breaking ribosome-nascent chain interactions (right diagram).
