Conserved mutation of Val-148 in RseA allowed retention of Site-2 cleavage. (A) Mutation of Val-148 to conserved, but not dissimilar or charged, amino acids in RseA allowed retention of Site-2 cleavage. DegS and OMP peptide were added together to the reactions where DegS is indicated. (B) Classification of three categories of amino acids at position 148 of RseA based on their impact on Site-1 and Site-2 cleavages. Mutation of Val-148 to any of the five amino acids—Glu, Asp, Gly, Pro, and Phe—crippled Site-1 cleavage of RseA by DegS. Among the mutations that allow Site-1 cleavage, six (mutation of Val-148 to Lys, His, Arg, Ser, Gln, and Tyr) do not allow Site-2 cleavage.