THE 26S-PROTEASOME - REGULATION AND SUBSTRATE RECOGNITION

There is extensive reprogramming of the ATPase regulators of the 26S p roteasome before the programmed elimination of the abdominal intersegm ental muscles (ISM) after eclosion in Manduca sexta [1]. This extensiv e ATPase reprogramming only occurs in ISM which are destined to die an d not in flight muscle (FM). The MS73 ATPase also increases in the pro leg retractor muscles which die at a developmentally different stage t o ISM. The non-ATPase regulator S5a shows a similar increase to the AT Pase regulators. We have cloned the Manduca SUG2 ATPase and shown that this ATPase is a component of the 26S proteasome. This ATPase shows a similar increase in concentration to the other ATPases in 26S proteas omes before muscle death. The SUG2 ATPase is also associated with othe r smaller complexes besides the 26S proteasome which act as activators of the 26S proteasome. Finally, in a yeast two-hybrid genetic screen we have identified a protein in human brain which interacts with the M S73 ATPase (and human S6). The interacting protein contains 6 ankyrin repeats and is co-immunoprecipitated with anti-MS73 antiserum after in vitro transcription/translation. The ankyrin repeat protein may inter act with the MS73 ATPase as part of the substrate recognition process by the 26S proteasome. Many proteins degraded by the 26S proteasome co ntain ankyrin repeats, e.g. IkB and some cyclins: binding through anky rin repeats to an ATPase regulator may complement protein ubiquitinati on and S5a binding as recognition signals by the 26S proteasome.