Activator complexes containing the proteasomal regulatory ATPases S10b (SUG2) and S6 ' (TBP1) in different tissues and organisms

Each 19S regulator of the 26S proteasome contains six ATPase subunits as we ll as many (>14) non-ATPase protein subunits. The ATPase subunits have been detected in other complexes which may regulate transcription and possibly other cellular processes. The S10b (yeast SUG2 or human p42) and the S6' (T BP1) ATPases have been found in an activator complex (modulator) prepared f rom bovine red cells. We have identified and partially characterised a simi lar activator from different human tissues (from soluble extracts of human brain, placenta and human embryonic kidney cells) and an insect: an activat or is present in soluble extracts of abdominal intersegmental muscle from M anduca sexta. Activation is ATP and concentration dependent. There is no st imulation of human red cell-derived 20S proteasome by the Manduca activator ruling out 11S regulator in the preparations. Additionally, cross-species activation occurs: the Manduca activator increases the activity of rat skel etal muscle 26S proteasomes and the human placental activator similarly inc reases the activity of 26S proteasomes prepared from muscles from Manduca s exta. Finally, there is no evidence for other ATPases in the activator comp lex.