Abstract: The meningococcal fhbp gene (encoding factor H binding protein) is naturally expressed from two independent transcripts by two differentially regulated promoters. In one transcript it is co-expressed with the neighbouring upstream gene from the Pnmb1869 promoter. The other transcript is monocistronic and is expressed from its own dedicated promoter, Pfhbp, which is activated by the global regulatory protein FNR in response to oxygen-limiting conditions. To increase expression of the monocistronic transcript a constitutively-active FNR mutant is used. The Pfhbp promoter can thus be activated, leading to over-expression of FNR-activated genes, such as fhbp.