Specific types of prosomes distribute differentially between intermediate and actin filaments in epithelial, fibroblastic and muscle cells

First observed as components of non-translated mRNP complexes, prosomes har bour RNase and several proteinase activities; they are also the central con stituent of the "Multicatalytic Proteinase (MCP) complexes" or "26S-proteas omes". In two recent publications (Arcangeletti et al,, 1997b; De Conto et al,, 1997) we have shown, by applying a new fixation technique, that these particles distribute differentially between the cytoskeletal networks of in termediate filament (IF) and actin types; previously they had been observed exclusively on the intermediate filaments. Here we further investigate the distribution of prosomes of several types, distinct by their subunit compo sition, between the IF of vimentin type and the actin network, as well as i n the 3D space of the cell. It is shown that subtypes of prosomes occupy sp ecific networks of the cytoskeleton, and that this pattern is specific for a given cell type. Confocal microscopy shows that prosome cytodistribution is not homogeneous in the 3D space: in the perinuclear area they colocalize most strongly with the IF, and more peripherally with the microfilament/st ress fiber system; connections may exist between the two networks. Furtherm ore, new data indicate that the prosome-actin interaction may participate i n the molecular structure of the stress fibers.