Mutational analysis of subunit i beta 2 (MECL-1) demonstrates conservationof cleavage specificity between yeast and mammalian proteasomes

Proteasomes are the major protein-degrading complexes in the cytosol and re gulate many cellular processes, To examine the functional importance of the MC14/MECL-1 proteasome active site subunits, cell lines expressing a catal ytically inactive form of MECL-1 were established. Whereas mutant MECL-1 wa s readily incorporated into cytosolic proteasomes, replacing the constituti ve MC14 subunit, removal of the prosequence was incomplete indicating that its processing required autocatalytic cleavage. Functional analyses showed that the absence of the MC14/MECL-1 active sites abrogated proteasomal tryp sin-like activity, but did not affect other catalytic activities. Our data demonstrate a conservation of cleavage specificity between mammalian and ye ast proteasomes. (C) 1999 Federation of European Biochemical Societies.