The 19S Regulatory Complex

The term proteasome is used to describe two kinds of multisubunit proteolytic complexes, the 26S and 20S, based on their sedimentation coefficient. The 26S proteasome degrades ubiquitinated protein substrates. The 26S complex contains the 20S as a core and regulatory caps on either end like a dumb bell. Each cap of the 26S proteasome is known as the 19S regulatory complex (19S RC). The 20S core is a cylindrical structure consisting of the catalytic part of the proteasome. ... 

Three other components that my laboratory has identified and partially purified from Fraction 2 of reticulocytes, termed CF1-CF3, are involved in the degradation of proteins ligated to ubiquitin [24]. These are apparently subcomplexes of the 26S proteasome, a large ATP-dependent protease complex first described by Re-chsteiner and co-workers [25], CF3 is identical to the 20S proteasome core particle [26], while CFl and CF2 may be similar to the base and lid subcomplexes of the 19S regulatory particle of the 26S proteasome, described more recently by the Finley laboratory [27], In hindsight, the reason for finding subcomplexes, rather than the complete 26S complex in Fraction 2 was technical we have routinely prepared Fraction 2 from ATP-depleted reticulocytes [20], under which conditions the 26S proteasome dissociates to its subcomplexes. We found that incubation of the three subcomplexes in the presence of ATP promotes their assembly to the 26S proteasome [24, 26]. The role of ATP in the assembly of the 26S proteasome complex remains unknown. 

In eukaryotic cells, the 20S proteasome assembles with one or two 19S regulatory complexes (RC) in an ATP-dependent manner to form the 26S proteasome (see Figure 1) (Hough et al. 1987 Ganoth et al. 1988 Driscoll and Goldberg 1990 Peters et al. 1994). The 26S holoenzyme is the most downstream element of the ubiquitin-proteasome pathway. 

The multicatalytic protease complex consists of a proteolytically active central core (core particle, 20S proteasome) and of a 19S regulatory complex which is attached to the core particle and is responsible for substrate recognition and unfolding. The spatial structure and the en2ymatic mecha-... 

W. Characterization of two subunits of Arabidopsis 19S proteasome regulatory complex and its possible interaction with the COP9 complex. J. Mol. Biol. 1999, 285, 85-95. 

Proteasome activity can also be regulated by substitution of subunits of the 20S core with subunits such as the ones induced by interferon-7 (IFN7). In addition, alternative regulatory complexes with different composition than the 19S RC can be attached to the 20S core, which alters the substrate specificity and activity of the proteasome (Figure 6(b)). ... 

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