Fig. 3. The formation of ubiquitin polymers by SCF^hFBH1 was catalyzed by either UbcH5a or UbcH5c but not by UbcH5b. (A) The ubiquitin ligase assay was performed with various E2 enzymes (Cdc34, UbcH5a, UbcH5b or UbcH5c). (B) The ubiquitin ligase assay was performed under addition of indicated E2 enzyme.