Figure 5. Mutagenesis at the proposed transacylation site. a) A stereodiagram of the top solution for PikACP6 and PikKS6 show residues in and around the interface targeted for mutational analysis (yellow). b) The model triketide lactone synthase,P1 -P6 -P7 , was employed to measure the effects of mutating individual residues on the surface of PikKS6 (*). Triketide lactone peak areas from LC/MS analysis (triplicate experiments, standard deviations shown) were made on media extracts from 8 d cultures (Data File 80). The KS residues whose sidechains are hypothesized to make the most contact with ACP, N275 and L315, were the most sensitive to mutation. Generally, mutations to positions farther from the proposed interface resulted in smaller losses in activity.