FIGURE 8.

The N termini of the 20 S α-subunits are essential for degradation of YFP-ssrA by the PAN-20 S complex. A, ATP-dependent β-casein degradation by PAN and the TA 20 S proteasome or Δ2–12 TA 20 S proteasome was monitored using the fluorescamine assay. B, left panel, YFP-ssrA degradation reaction in the presence of wild type TA 20 S proteasome (blue) and Δ2–12 TA 20 S proteasome (red) in the presence and absence of ATP. Right panel, unfolding reaction of YFP-ssrA by PAN. In the presence of ATP some loss of YFP-ssrA fluorescence is detected (blue). The fluorescence loss is only partially due to the constant and contrasting unfolding-refolding reactions and represents the dynamic, steady state equilibrium.