The results described above led us to reexamine the role of MK biosynthesis in intracellular survival of L. monocytogenes. MK is synthesized from chorismate, the end product of the shikimate biosynthesis pathway, by eight well-characterized enzymes encoded by the men genes (23) (Fig. 6A). Following conversion of o-succinylbenzoyl-CoA (OSB-CoA) to 1,4-dihydroxy-2-naphthoyl-CoA (DHNA-CoA) by MenB, an unknown DHNA-CoA thioesterase is predicted to convert DHNA-CoA to 1,4-dihydroxy-2-naphthoate (DHNA) (35). MenA and MenG are responsible for the final two steps in MK biosynthesis by addition of the polyprenyl side chain and methylation of the naphthoquinone ring, respectively (Fig. 6A).