As we known, proteases can be divided into endo- and exo-peptidases. Also, based on their active site, they divided into cysteine, serine, aspartic and metallo proteases. Does the proteasome (26S or/and 20S) involued in ubiquitin-dependent proteolysis follow the above rule? If yes, what does it belong to? Pease give me a mail. Thanks. Wejin