CrgA is an inducible LysR-type regulator of Neisseria meningitidis, acting both as a repressor and as an activator of gene transcription

The crgA gene of Neisseria meningitidis, which codes for a LysR-type regulator, is divergently oriented with respect to the mdaB gene, which codes for a hypothetical NADPH-quinone oxidoreductase. Transcriptional studies of the intergenic region between crgA and mdaB showed that two overlapping and divergent promoters, P-crgA and P-mdaB, control transcription of these genes. Deletion of the crgA gene led to a strong increase in transcription from the P-crgA promoter and a concomitant strong decrease in transcription from the P-mdaB promoter, indicating that CrgA acts both as an autorepressor of transcription at its own promoter and as an activator of transcription at the mdaB promoter. Addition of alpha-methylene-gamma-butyrolactone (MBL), an inducer of NADPH-quinone oxidoreductase, to wild-type N. meningitidis cells specifically resulted in further activation of transcription of the P-mdaB promoter and more repression of transcription of the P-crgA, promoter. No such regulation was observed when MBL was added to crgA-deficient cells, indicating that the transcriptional response to MBL is CrgA mediated. Under the same experimental conditions, no regulation of transcription by either CrgA or MBL was detected at the pillus and capsule genes. The role of CrgA in the regulation of gene expression during the infectious cycle of N. meningitidis is discussed.