Localization of the histidine kinase PilS to the poles of Pseudomonas aeruginosa and identification of a localization domain

Transcription of the type IV pilus subunit gene of Pseudomonas aeruginosa i s controlled by a two-component signal transduction system. PilS, the histi dine kinase, is membrane bound and PilR, its cognate response regulator, is cytoplasmic. The signal that activates PilS is unknown. PilS has three dom ains: (i) The N-terminus, predicted to form six transmembrane (TM) helices; (ii) a central linker domain; and (iii) the C-terminal transmitter domain containing all the conserved residues of sensor kinases. A translational fu sion of the gfp gene (green fluorescent protein) to the 3' end of pilS was used to determine the position of PilS in the bacterial cell. Epifluorescen ce microscopy revealed that PilS is retained to the poles of P. aeruginosa but is distributed evenly about the membrane of Escherichia coli. Deletions of the PilS-GFP fusion revealed that the TM domain was sufficient and nece ssary to bring GFP to the membrane of P. aeruginosa and E. coli but was not sufficient to confine GFP to the poles. Retention to the poles of P. aerug inosa required both the TM and linker domains. Replacement of the PilS TM d omain with an E. coli membrane protein, MalG, still allowed polar localizat ion. Therefore, the PilS TM domain positions the linker domain close to the membrane allowing it to interact with the putative polar anchor which is s pecific to P. aeruginosa.