Ribosomal tunnel and translation regulation

This review describes the results of recent studies of the ribosomal tunnel (RT), the major function of which is to allow the smooth passage of nascent polypeptides with different sequences from the peptidyl transferase center of the ribosome to the tunnel exit, where the folding of protein molecules begins. The features of structural organization of RT and their role in modulation and stabilization of the nascent chain conformation are discussed. Structural features of macrolide binding sites as well as application of macrolide antibiotics and their derivatives as tools to investigate ligand-tunnel wall interactions are also considered. Several examples of strong and specific interactions of regulatory polypeptides with nucleotide and amino acid residues of RT that lead to ribosome stalling and translational arrest are described in detail. The role of these events in regulation of expression of certain genes is discussed on the basis of recent high-resolution structural studies of nascent chains in the RT.