THE PILG GENE-PRODUCT, REQUIRED FOR PSEUDOMONAS-AERUGINOSA PILUS PRODUCTION AND TWITCHING MOTILITY, IS HOMOLOGOUS TO THE ENTERIC, SINGLE-DOMAIN RESPONSE REGULATOR CHEY

The Pseudomonas aeruginosa pilG gene, encoding a protein which is invo lved in pilus production, was cloned by phenotypic complementation of a unique, pilus-defective mutant of strain PAO1. This mutant, designat ed FA2, although resistant to the pilus-specific phage D3112 was sensi tive to the pilus-specific phages B3 and F116L. In spite of the unusua l phage sensitivity pattern, FA2 lacked the ability to produce functio nal polar pili (pil) and was incapable of twitching motility (twt). Ge netic analysis revealed that the FA2 pil mutation, designated pilG], m apped near the met-28 marker located at 20 min and was distinct from t he previously described pilT mutation. This map location was confirmed by localization of a 6.2-kb EcoRI fragment that complemented FA2 on t he SpeI and DpnI physical map of the P. aeruginosa PAO1 chromosome. A 700-bp region encompassing the pilG gene was sequenced, and a 405-bp o pen reading frame, with characteristic P. aeruginosa codon bias, was i dentified. The molecular weight of the protein predicted from the amin o acid sequence of PilG, which was determined to be 14,717, correspond ed very closely to that of a polypeptide with the apparent molecular w eight of 15,000 detected after expression of pilG from the T7 promoter in Escherichia coli. Moreover, the predicted amino acid sequence of P ilG showed significant homology to that of the enteric CheY protein, a single-domain response regulator. A chromosomal pilG insertion mutant , constructed by allele replacement of the wild-type gene, was not cap able of pilus production or twitching motility but displayed normal fl agellum-mediated motility. These results, therefore, suggest that PilG may be an important part of the signal transduction system involved i n the elaboration of P. aeruginosa pili.