Fig. 1.

Co-translational folding is a stepwise vectorial process proceeding in most of the cases from the N- to C-terminal end of the growing polypeptide chain. The appearance of distinct folding intermediates is linked to the overall and local rates of translation. The process begins very early during polypeptide chain synthesis on the ribosome, with some secondary structure elements (such as e.g., alpha-helices) forming inside the ribosomal tunnel (and some tertiary structures forming inside the vestibule (lower/wider) region of the ribosomal exit tunnel. The tertiary structure of the protein is nearly formed at the end of the protein synthesis.