The ubiquitin system for protein degradation.

PERSPECTIVES AND SUMMARy 762 INTRODUCTION 762 ENZYMES OF UBIQUITIN ACTIVATION AND LIGATION 764 Ubiq u it in -Activatin g En zyme, E } . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . 764 Ubiquitin-Carrier Proteins, E2s 767 Ubiq uit in -Protein Ligases, E3s.. ... ........ ... . ... . .... .. . 771 DEGRADATION OF PROTEINS LIGATED TO UBIQUITIN 775 The 26S Protease Complex and its Three Components 775 Identification of CF-3 as the 20S P rotea se Complex . . . . . . . . . . . . . . . . . .... . . . .. . .... . . . . . . . 777 P ossible Role s of ATP 780 UBIQUITIN-C-TERMINAL HYDROLASES 781 SIGNALS IN PROTEINS FOR UBIQUITIN-MEDIATED DEGRADATION 786 The N-Term ina l Recognition Signa l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . 786 Sign als t hat are Distinct from the N-Term in al Re sid ue .... . . ......... 790 DEGRADATION OF SPECIFIC CELLULAR PROTEINS BY THE UBIQUITIN SYSTEM: REGULATORY ASPECTS 792 P hytochrome . . . . .. . . . . . . . 792 Oncoprotein s. . ... . .... . . .... ....... . ..... .... ..... ..... . ... . ........ . ...... ......... . ... 794 MATaJ. Repre ssor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795 Cyclin s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 796 DIVERSE FUNCTIONS OF UBIQUITIN CONJUGATION.. 799 CONCLUDING REMARKS 801