Nucleotide sequence and transcriptional initiation site of two Pseudomonas aeruginosa pilin genes

The complete nucleotide sequences of the 1.2-kilobase HindIII fragments which contain the pilin genes of two independently isolated strains of Pseudomonas aeruginosa (PAK and PA103) have been determined and compared to that of strain PA01 (Sastry, P. A., Finlay, B. B., Pasloske, B. L., Paranchych, W., Pearlstone, J. R., and Smollier, L. B. (1985) J. Bacteriol. 164, 571-577). The fragments share extensive regions of homology, including the 5'- and 3'-flanking sequences as well as the 5' end of the pilin gene. The most highly diverged segments of the pilin genes are those which encode the variable carboxyl-terminal region of the pilin polypeptides. The pilin polypeptides each contain a 6-amino acid amino-terminal leader peptide (Met-Lys-Ala-Gln-Lys-Gly) and are nearly identical in the following 60 amino acids. The carboxyl-terminal portion of the pilin polypeptides contain extensive regions of divergence in their amino acid sequences, although hydropathicity analysis of the pilin polypeptides indicated that they are structurally similar. The transcriptional initiation site of the PAK pilin gene has been determined by S1 nuclease mapping. The promoter region at -10 and -35 base pairs from the transcriptional initiation site shows no significant homology to the consensus Escherichia coli promoter, but the -12 and -24 regions show a high degree of homology to promoters which require the ntrA gene product for transcription. Several other Pseudomonas promoters and the promoters of the homologous pilin genes from other bacterial species also share homology to this sequence.