Fig. 6. The role of the N-terminus in ClpXP-mediated degradation of UmuD′. UmuD (squares) and UmuD9-4 (triangles) peptides, at the concentrations indicated, were incubated with UmuD′ at 25°C for 30 min, followed by the addition of ClpXP. After addition of ClpXP the reactions were incubated at 37°C for 1 h and the samples were electrophoresed on a 16% polyacrylamide gel. Samples were processed, visualized and quantitated as described in Figure 1. These experiments reveal that the N-terminal 24 amino acids of UmuD are sufficient to target UmuD′ for ClpXP-mediated proteolysis.