In prokaryotes,ubiquinone and menaquinone (MK) are obligatory component of the electron-transfer pathway.Escherichia coli,which is a facultative anaerobe,utilizes ubiquinone under aerobic conditions,but uses MK 8 when it is grown anaerobically.By contrast,many Gram-positive aerobes such as Streptomyces strains contain only MKs.MK biosynthesis is therefore essential for the survival of these strains.In E.coil,MK is biosynthesized from chorismate bv seven enzvmes (MenA MenG) [1,2].