Fig. S3.

E. coli Lon is active to degrade a model substrate. The I27 domain of human titin (a common small model protein used in unfolding and degradation experiments) tagged with 20 amino acids of SulA C-terminal region (a Lon degron) (titin-sulA20) was used as a positive control substrate (10, 23) to confirm that both B. subtilis LonA and E. coli Lon are active under the same conditions used for PerR degradation in Fig. 2. Both Lon orthologs degraded the control substrate with a similar efficiency.