Transcriptional control of gonococcal pilE expression: involvement of an alternate sigma factor

The pilE gene encoding Neisseria gonorrhoeae (Gc) pilin contains two putative promoter sequences 5' to the transcription start point (tsp), a Pribnow box and an RpoN-binding consensus sequence. Sequence analysis shows that the nucleotide (nt) sequence of the pilE promoter region is completely conserved among eight different Gc isolates. Using a pilE::lacZ transcriptional fusion, we demonstrate that the RpoN σ factor can function in Escherichia coli to increase pilE transcription when the NifA activator from Klebsiella is present in trans. In addition, over-production of the native pilin protein using RpoN and NifA is lethal to E. coli. Finally, we show that the RpoN σ factor decreases the basal expression of pilE when an activator is not present. These results suggest that, in Gc, pilE transcription may be regulated by RpoN in conjunction with an activator and that σ⁷⁰ can also act to direct transcription of pilE.