Menaquinone (vitamin K2) biosynthesis: localization and characterization of the menE gene from Escherichia coli

In Escherichia coli, the biosynthesis of the electron carrier menaquinone (vitamin K2) involves at least seven identified enzymatic activities, five of which are encoded in the men cluster. One of these, the conversion of o-succinylbenzoic acid to 1,4-dihydroxy-2-naphthoic acid, requires the formation of o-succinylbenzoyl-CoA (OSB-CoA) as an intermediate. Formation of the intermediate is mediated by OSB-CoA synthetase encoded by the menE locus known to be located either 5' of menB, or 3' of menC. A DNA fragment overlapping the 3' end of menC in shown by enzymatic complementation to elevate OSB-CoA synthetase activity. Nucleotide sequence analysis of the fragment identified a 1.355-kb open reading frame (ORF) which, when deleted at either the 5' or 3' end, failed to generate increased enzymatic activity. The ORF is preceded by a consensus ribosome-binding site, but no apparent sigma-70 promoter. An oppositely transcribed unidentified gene cluster follows the menE ORF. The region 5' of menB contains an an additional ORF of unknown function (orf241) and establishes the order of genes in the men cluster as menD, orf241, menB, menC and menE. All loci are transcribed counter-clockwise.