“…In contrast to the initial suggestion that the tunnel interior is inert in terms of interactions with the nascent polypeptide (Nissen et al, 2000), in reality, the tunnel interacts with nascent polypeptide chains, thus contributing to biological regulation (Chiba et al, 2009; Gong and Yanofsky, 2002; Ishii et al, 2015; Nakatogawa and Ito, 2002; Onouchi et al, 2005; Yanagitani et al, 2011, Ito and Chiba, 2013). Cryo-EM structures of ribosomes stalled by ribosome arresting peptides (RAPs) have revealed a range of interactions between the nascent chains and the ribosomal interior components at the PTC and/or the exit tunnel, such as the uL22/uL4 constriction site (Bhushan et al, 2011; Seidelt et al, 2009; Shanmuganathan et al, 2019; Sohmen et al, 2015; Su et al, 2017). Recent analyses using ribosome profiling (Dao Duc and Song, 2018; Han et al, 2020; Requião et al, 2016; Sabi and Tuller, 2015) and direct detection of accumulating peptidyl-tRNAs (Chadani et al, 2016) have suggested the widespread occurrence of translation pausing, to which nascent polypeptides may contribute.…”