RELATED ORGANELLES OF THE ENDOSOME-LYSOSOME SYSTEM CONTAIN DIFFERENT REPERTOIRE OF UBIQUITINATED PROTEINS IN SF9 INSECT CELLS

Two components of the endosomal/lysosomal compartment of Sf9 cells, mu ltivesicular bodies (MVB) and light vacuoles with membrane complexes ( LVMC) have been isolated and probed for ubiquitin protein conjugates w ith a specific antibody. Immunogold electron microscopy indicates that whereas ubiquitin-protein conjugates are localised to electron dense areas of MVB they are associated with the membranes of LVMC. Five ubiq uitinated polypeptides are revealed in MVB by immunoblotting while num erous ubiquitinated species forming a smear following electrophoresis are present in LVMC. We suggest two possible routes for entry of ubiqu itin-protein conjugates into these organelles, via the cell surface an d via primary lysosomes.