Summary: The primary structure of a 2671 bp DNA fragment between the gene (encoding plasminogen activator) and the origin of replication of the wild-type plasmid pYP358 was determined. Two ORFs of 1074 and 426 bp with opposite transcription polarities were identified on both strands. They encode a 357 aa pesticin activity protein (Pst) and a 141 aa pesticin immunity polypeptide (Pim). A GC-rich palindromic structure located between and can form a hairpin loop and serve as a rho-independent transcription terminator sequence for both genes. The site for the interaction with the LexA repressor of the SOS system was found in another palindromic structure preceding the structural gene. A deduced 39.9 kDa Pst polypeptide is devoid of a signal peptide, indicating a Sec-independent mode of export. Pst carries a pentapeptide typical of TonB-dependent colicins (TonB box) that is necessary for the interaction with the yersiniabactin/pesticin receptor and for active energy-dependent transport through the outer membrane. The substitution of the last five C-terminal amino acids did not significantly influence the bactericidal activity of the truncated pesticin. The pesticin lost its ability to kill sensitive bacteria and to bind to a pesticin receptor after deletion of the last 57 C-terminal amino acids. A deduced 16 kDa Pim protein has an N-terminal hydrophobic amino acid stretch with features typical of prokaryotic signal peptides. Pim is a slightly hydrophilic protein with a basic pl. The immunity protein was localized in the periplasmic space and in the outer-membrane fraction after its overexpression under the polymerase T7 promoter. Several other ORFs were identified on the sequenced 2671 bp fragment, but none of them seemed to encode a typical lysis peptide, which is necessary for the release of the pesticin. In the promoter region and in the regions preceding and following the operon, the DNA sequence has high (< 70%) identity with other colicin genes. The DNA sequence located 284 bp upstream of the gene showed more than 90% similarity to antisense RNA I of the ColE1 replicon. This defined the location of the pYP358 origin of ColE1-type replication.


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