The mechanism of protein folding is presented, which can account for the thermodynamical phase transition and the rapidity of folding process. The long-range feature of hydrophobic interaction and its specificity after the formation of the secondary structures play the essential role in folding. The refoldings of flavodoxin, erabutoxin and BPTI (bovine pancreatic trypsin inhibitor) are discussed. Finally a possible mechanism of folding in membrane proteins is proposed, and applied to bacteriorhodopsin.
