LOCALIZATION OF PNT22 70KDA HEAT-SHOCK COGNATE-LIKE PROTEIN IN THE PLASMA-MEMBRANE

It has been argued that 70 kDa heat shock cognate (hsc73)-like molecul es may be expressed on the surface of certain cells, but direct eviden ce of this has yet to be found. To clarify whether this molecule belon gs to hsc73 itself, the membrane protein fraction of Daudi cells was i solated by Triton X-114 phase separation and the reactivity of this me mbrane protein fraction was assessed with monoclonal antibodies (mAbs) which react with 70 kDa heat shock protein (hsp) family, i.e., NT22, A15 and 3A3. In western blotting analysis, mAb NT22-defined protein (p NT22) was clearly detected as a membrane protein of Daudi cells with a n approximate molecular size of 70 kDa, whereas pNT22 was not recogniz ed by anti-cytoplasmic hsc73/hsp72 mAbs A15 or 3A3. By using deleted r ecombinant hsc73 proteins, it was determined that mAb NT22 recognizes the N-terminal 350-372 amino acid stretches of the hsc73 protein. mAb NT22 also reacted with the cell surface protein of Daudi cells in FAGS analysis. Taken together, our present data strongly suggest that pNT2 2 may be a novel hsc73-like protein that is localized in the plasma me mbrane.