Cloning and characterization of the Neisseria gonorrhoeae MS11 folC gene

The gene coding for folylpoly-(gamma)-glutamate synthetase (FPGS)-dihydrofolate synthetase (DHFS) of Neisseria gonorrhoeae (Ngo) has been cloned by functional complementation of an Escherichia coli folC mutant (SF4). The sequence encodes a 224-residue protein of 46.4 kDa. It shows 46% identity to the E. coli FPGS-DHFS and 29% identity to the FPGS of Lacto-bacillus casei. Sequence comparisons between the three genes reveal regions of high homology, including ATP binding sites required for bifunctionality, all of which may be important for FPGS activity. In contrast to L. casei FPGS, the E. coli and Ngo enzymes share some additional regions which may be essential for DHFS activity. The products of Ngo folC and flanking genes were monitored by T7 promoter expression. Interestingly, deletion of the upstream folI gene, which encodes a 16.5 kDa protein, abolishes the capacity of folC to complement E. coli SF4 to the wild-type phenotype. The ability to complement can be restored by folI provided in trans. Unlike folC mutants, gonococcal folI mutants are viable and display no apparent phenotype. Thus, in contrast to E. coli, Ngo folC is expressed at a sufficiently high level from its own promoter, in the absence of FolI This study provides the first insights into the genetic complexity of one-carbon metabolism in Nqo.