title: Distinct 19 S and 20 S subcomplexes of the 26 S proteasome and their distribution in the nucleus and the cytoplasm.
abstract: The 26 S proteolytic complex ("26 S proteasome") is a macromolecular assembly thought to be involved in ATP- and ubiquitin-dependent protein degradation in the cytoplasm of higher eukaryotic cells. This complex is composed of one 20 S cylinder particle (multicatalytic proteinase, 20 S proteasome) and two cap-shaped 19 S particles comprising a set of polypeptides in the M(r) range of 35,000-110,000. Here we show that cell supernatant fractions contain both these two subunit complexes as distinct particles as well as assembled to 26 S proteasomes. We have separated and purified all three forms from Xenopus laevis oocytes and have determined their peptidase and protease activities. Using various antibodies specific for either a constitutive p52 polypeptide of the 19 S cap complex or for proteins of the 20 S cylinder particle, we have immunolocalized these complexes in both the cytoplasm and the nucleus of diverse species and cell types. The occurrence of all three forms, the 26 S proteasome, the 20 S cylinder particle, and the 19 S cap complex in the nucleoplasm has also been demonstrated in analyses of isolated giant nuclei from Xenopus oocytes. In addition, we show that the 19 S and 20 S subcomplexes can be released from 26 S proteasomes by ATP depletion and that readdition of ATP to 19 S and 20 S particles in cell extracts leads to the reformation of 26 S proteasomes. We discuss that all three particles (19 S, 20 S, and 26 S) exist in a dynamic equilibrium in both cell compartments and serve cytoplasmic as well as nucleus-specific functions.
authors.affiliation: Division of Cell Biology, German Cancer Research Center, Heidelberg.
authors.forename: J M
authors.initials: JM
authors.lastname: Peters
authors.forename: W W
authors.initials: WW
authors.lastname: Franke
authors.forename: J A
authors.initials: JA
authors.lastname: Kleinschmidt
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002467:Cell Nucleus / Q000201:enzymology*; D002852:Chromatography, Ion Exchange; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D003593:Cytoplasm / Q000201:enzymology*; D004591:Electrophoresis, Polyacrylamide Gel; D008856:Microscopy, Fluorescence; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D009865:Oocytes / Q000201:enzymology; D046988:Proteasome Endopeptidase Complex; D014982:Xenopus laevis
chemical_list: D009097:Multienzyme Complexes; D000255:Adenosine Triphosphate; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex