(Science: cell biology) cytoplasmic proteins of both prokaryotes and eukaryotes that bind to nascent or unfolded polypeptides and ensure correct folding or transport. Chaperone proteins do not covalently bind to their targets and do not form part of the finished product. Heat-shock proteins are an important sub set of chaperones. Three major families are recognised, the chaperonins (groEL and hsp60), the hsp70 family and the hsp90 family. Outside these major families are other proteins with similar functions including nucleoplasmin, secB and T-cell receptor associated protein.