MOLECULAR CHARACTERIZATION OF PYOCIN S3, A NOVEL S-TYPE PYOCIN FROM PSEUDOMONAS-AERUGINOSA

The genetic determinant for the soluble pyocin S3 was isolated from a genomic library constructed in the plasmid pGV1122, of Pseudomonas aer uginosa strain P12 isolated from a cystic fibrosis patient. The nucleo tide sequence of a 3270-base pair DNA fragment was determined, and the two structural genes, pyoS3A and pyoS3I, and the 3'- and 5'-flanking regions were localized. Transcription (Northern blot) analysis showed that the two genes were co-transcribed. The genes pyoS3A and pyoS3I co de for polypeptides of 767 and 154 amino acids, respectively, with cal culated molecular weights of 81,385 and 17,047. Pyocin S3 was produced in Escherichia coli from a plasmid and purified as a complex of two c omponents (S3A and S3I) corresponding to the pyoS3A and pyoS3I gene pr oducts, respectively. The S3A component, like pyocin S3, had a killing effect involving DNase activity and was inhibited by the S3I protein. Comparisons of the predicted amino acid sequence of the two component s of pyocin S3 to those of pyocins S1, S2, and AP41 indicate that pyoc in S3 is a new type of S-type pyocin.