Localization of proteasomal antigens during different phases of the cell cycle in HeLa cells

We localized two different proteasome-associated epitopes with the use of two specific monoclonal antibodies, MCP21 and anti-p25, in interphase and mitotic HeLa cells cultured in vitro. We provide evidence for an association of those antigens with the spindle poles in metaphase and with the midbody region in anaphase and telophase. Triton-nonextractable structures are also labeled in interphase. Moreover, the labeling pattern of interphase cells obtained with the monoclonal antibodies MCP21 and anti-p25 differs considerably, and in the case of MCP21 displays clear cell cycle-specific changes: nuclear labeling is absent or very weak in G₁ and S phases of the cell cycle, whereas it is strong in G₂ phase. This might reflect the existence of different subpopulations of proteasomes in the cell.