For branched chain amino acid synthesis, microorganisms such as Corynebacterium glutamicum employ feedback inhibition of the critical enzyme acetohydroxy acid synthase (AHAS) by leucine, isoleucine, and valine (Elisakova et al., Appl Env Micro 2005) (Table 1 and Figure 1). The activity of AHAS is inhibited by any of the three amino acids to 50% of the maximum. However, the inhibitory effect does not exceed 50% even in the presence of all three amino acids. C. glutamicum is used for commercial production of a number of amino acids including valine. AHAS from this organism is comprised of a catalytic and a regulatory subunit encoded by the ilvB and ilvN genes, respectively. Elisakova and collaborators identified mutations in the regulatory subunit of C. glutamicum that conferred resistance to feedback inhibition. 

E.   Figure 2 shows the amount of L-valine produced in various mutants. Which combination of gene mutations would you include in a strain to boost L-valine production to maximal levels? Explain your rationale using the pathway described in Figure 1.

I know the answer is the ilvA/panB/ilvNM13 one but I don’t know how to explain my answer using the pathway.