Practice question

Completion of protein synthesis releases nascent chain through polypeptide exit tunnel traversing core of large subunit from peptidyl transferase center to solvent-exposed surface, spanning about 100 angstroms. Tunnel walls built from segments of 23S or 28S rRNA and constriction proteins L4, L22, L23 regulate folding, permit alpha-helix formation inside, and provide binding platform for chaperones like trigger factor, signal recognition particle SRP, and modification enzymes NAC and methionine aminopeptidase that act co-translationally to target or process emerging polypeptide for secretion and membrane insertion.