Fig. 6. GFP degradation by T.acidophilum 20S proteasome mutants activated by M.jannaschii PAN. Proteasomes mutated at a single residue are denoted r10a for the Arg10 to Ala proteasome, etc. Proteasomes mutated in both Tyr8 and Asp9 are denoted aa, gg and dy, for the AlaAla, GlyGly and AspTyr substitutions. Proteasomes for which residues 2–7 or 2–12 were deleted are denoted Δ(2–7) and Δ(2–12). (A) Representative data for wild-type and mutant proteasomes that show high activity. The r10a mutant is included in this panel because, although it shows somewhat reduced activity compared with wild type, it is still much more active than mutations of the invariant cluster residues. Degradation of His₆-GFP–ssrA is followed by western blot using anti-His antibodies. The top band in each panel is the substrate. The lower band is the His₆-tagged proteasome β-subunit. Time in minutes is indicated above. (B) Same as (A) for proteasomes that show low activity.