PROTEASOME FUNCTION IS DISPENSABLE UNDER NORMAL BUT NOT UNDER HEAT-SHOCK CONDITIONS IN THERMOPLASMA-ACIDOPHILUM

Hitherto the biology of proteolysis in prokaryotes, particularly in ar chaea, is only poorly understood. We hale used the tri-peptide vinyl s ulfone inhibitor carboxybenzyl-leucyl-leucyl-leucine vinyl sulfone (Z- L-3 VS) to study the in vivo function of proteasomes in Thermoplasma a cidophilum. Z-L-3 VS is a potent inhibitor of the Thermoplasma proteas ome and is capable of modifying 75 to 80% of the proteasomal beta-subu nits in cell cultures. Inhibition of proteasomes has only marginal eff ects under normal growth conditions. Under heat shock conditions, howe ver, the effects of proteasome inhibition are much more severe, to the extent of complete cell growth arrest. These data suggest that other proteolytic systems may exist that can compensate for the loss of prot easome function in T. acidophilum. (C) 1998 Federation of European Bio chemical Societies.