Formation of pilin in Pseudomonas aeruginosa requires the alternative sigma factor (RpoN) of RNA polymerase.

The promoter region of the Pseudomonas aeruginosa pilin gene has a high degree of similarity to the nitrogen-regulated promoters of enteric bacteria. These promoters are recognized by the alternative sigma factor of RNA polymerase, termed RpoN (NtrA or GlnF). This observation suggested that the P. aeruginosa pilin gene may be transcribed by the RpoN-containing RNA polymerase. We, therefore, cloned the RpoN gene from P. aeruginosa into Escherichia coli (where it formed a functional product) and used that cloned gene to construct a mutant of P. aeruginosa that was insertionally inactivated in its RpoN gene. This mutant failed to synthesize pilin, indicating that the RpoN sigma factor is required for transcription of the pilin gene.