The 26S proteasome is a large multisubunit complex involved in degrading both 
cytoplasmic and nuclear proteins. We have investigated the subcellular 
distribution of four regulatory ATPase subunits (S6 (TBP7/MS73), S6' (TBP1), S7 
(MSS1), and S10b (SUG2)) together with components of 20S proteasomes in the 
intersegmental muscles (ISM) of Manduca sexta during developmentally programmed 
cell death (PCD). Immunogold electron microscopy shows that S6 is located in the 
heterochromatic part of nuclei of ISM fibres. S6' is present in degraded 
material only outside intact fibres. S7 can be detected in nuclei, cytoplasm and 
also in degraded material. S10b, on the other hand, is initially found in nuclei 
and subsequently in degraded cytoplasmic locations during PCD. 20S proteasomes 
are present in all areas where ATPase subunits are detected, consistent with the 
presence of intact 26S proteasomes. These results are discussed in terms of 
heterogeneity of 26S proteasomes, 26S proteasome disassembly and the possible 
role of ATPases in non-proteasome complexes in the process of PCD. Cell Death 
and Differentiation (2000) 7, 1210 - 1217.