Dynamics of proteasome distribution in living cells

EMBO J. 1997 Oct 15;16(20):6087-94. doi: 10.1093/emboj/16.20.6087.


Proteasomes are proteolytic complexes involved in non-lysosomal degradation which are localized in both the cytoplasm and the nucleus. The dynamics of proteasomes in living cells is unclear, as is their targeting to proteins destined for degradation. To investigate the intracellular distribution and mobility of proteasomes in vivo, we generated a fusion protein of the proteasome subunit LMP2 and the green fluorescent protein (GFP). The LMP2-GFP chimera was quantitatively incorporated into catalytically active proteasomes. The GFP-tagged proteasomes were located within both the cytoplasm and the nucleus. Within these two compartments, proteasomes diffused rapidly, and bleaching experiments demonstrated that proteasomes were transported slowly and unidirectionally from the cytoplasm into the nucleus. During mitosis, when the nuclear envelope has disintegrated, proteasomes diffused rapidly throughout the dividing cell without encountering a selective barrier. Immediately after cell division, the restored nuclear envelope formed a new barrier for the diffusing proteasomes. Thus, proteasomes can be transported unidirectionally over the nuclear membrane, but can also enter the nucleus upon reassembly during cell division. Since proteasomes diffuse rapidly in the cytoplasm and nucleus, they may perform quality control by continuous collision with intracellular proteins, and degrading those proteins that are properly tagged or misfolded.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antigen Presentation
  • Biological Transport
  • Cell Compartmentation
  • Cell Division
  • Cell Nucleus / metabolism
  • Cysteine Endopeptidases / genetics
  • Cysteine Endopeptidases / metabolism*
  • Cytoplasm / metabolism
  • Green Fluorescent Proteins
  • Humans
  • Luminescent Proteins / genetics
  • Luminescent Proteins / metabolism
  • Microscopy, Fluorescence
  • Movement
  • Multienzyme Complexes / genetics
  • Multienzyme Complexes / metabolism*
  • Proteasome Endopeptidase Complex
  • Proteins / genetics
  • Proteins / metabolism*
  • Recombinant Fusion Proteins / metabolism
  • Tumor Cells, Cultured


  • Luminescent Proteins
  • Multienzyme Complexes
  • Proteins
  • Recombinant Fusion Proteins
  • LMP-2 protein
  • Green Fluorescent Proteins
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex