Before a newly translated polypeptide can be active, it must be folded into the proper three-dimensional structure and it may have to associate with other subunits.

At the beginning of translation, the first 30 amino acids are protected before they begin to emerge from the ribosome. There is good evidence that folding actually begins during translation and in most cases is nearly complete by the time the chain is released. For example, antibodies against the tertiary structure (that is, the folded structure) of the galactosidase protein will bind to polyribosomes (see here) in the midst of translation.

This spontaneous folding during translation may be blocked or delayed, however, by chaperone proteins.