Phosphorylation and functional analysis of PilA, a protein involved in the transcriptional regulation of the pilin gene in Neisseria gonorrhoeae.

The transcriptional regulation of the pilE gene, coding for the pilin in Neisseria gonorrhoeae, by PilA/PilB proteins is quite complex. Sequence analysis of PilA suggested that it has multiple domains. PilA appears to have in its N-terminal half a DNA-binding site followed by a region showing sequence similarity with other bacterial transcriptional regulators. In its C-terminal half, PilA has extensive homology with the 54 kDa protein of the eukaryotic signal-recognition particle which is involved in protein secretion. A transcriptional fusion between the promoter of pilE and the lacZ gene was constructed and integrated into the gonococcal chromosome. We show that transcription of the pilE-lacZ fusion is affected in pilA mutants in the absence of any possible interference with pilin secretion. Moreover, pilE transcription depends on a -24/-12-type promoter which could be a member of a family of promoters recognized by the alternative sigma subunit, RpoN, of the RNA polymerase. We also show that PilA binds specifically to the promoter region of pilE and that it is phosphorylated in a manner dependent on acidic residues Glu-59, Asp-149 and Asp-186. The functional organization of PilA suggests that it may be an unusual transcriptional regulator different from other RpoN-dependent activators.