Figure 5.

Several Lys Residues Are Ub-Acceptor Sites, and Their Mutation Affects 66K Stability.

(A) and (B) Arabidopsis protoplasts were cotransfected with expression vectors encoding myc₂-Ub and various 66K mutants as indicated. Formation of poly-Ub-66K conjugates was determined by immunoprecipitation as in Figure 4. The amount of 66K present in the immunoprecipitates was determined by immunoblotting (IB).

(C) Effect of mutation of Lys to Arg on the stability of 66K-LUC, measured using the UPR assay as in Figure 2.