FIGURE 4: Polyamines do not enhance the degradation of ubiquitin-dependent substrates by the proteasome.

(A) Western blot analysis of steady state levels of two ubiquitin-dependent substrates, namely, a substrate of the N-end rule pathway (Ub-R-e^k-Ha-URA3) and a substrate of the UFD pathway (Ub-V76- e^k-Ha-URA3). Experiments were done as described for Fig. 3A. Ha signals were quantified, normalized to the Cdc11 loading controls, and given relative to the level of protein without spermidine, which was set to 100%. Error bars, s.d.; n = 2.

(B) Assay of chymotrypsin-like activity with purified proteasome (same material as shown in Fig. 2A) in the presence of increasing spermine (spm) concentrations. Error bars, s.d.; n = 4.