Localisation of 26S proteasomes with different subunit composition in insect muscles undergoing programmed cell death

The 26S proteasome is a large multisubunit complex involved in degrading bo th cytoplasmic and nuclear proteins. We have investigated the subcellular d istribution 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 p rogrammed cell death (PCD). Immunogold electron microscopy shows that S6 is located in the heterochromatic part of nuclei of ISM fibres. S6' is presen t in degraded material only outside intact fibres. S7 can be detected in nu clei, cytoplasm and also in degraded material, S10b, on the other hand, is initially found in nuclei and subsequently in degraded cytoplasmic location s during PCD. 20S proteasomes are present in all areas where ATPase subunit s are detected, consistent with the presence of intact 26S proteasomes. The se results are discussed in terms of heterogeneity of 26S proteasomes, 26S proteasome disassembly and the possible role of ATPases in non-proteasome c omplexes in the process of PCD.