Summary: A novel klebicin, klebicin B, produced by an isolate of has been identified. It is encoded by a 5.5 kb plasmid, pKlebB-K 17/80, which is mobilized into UNF5023 by a large plasmid found in the same strain. The 5.5 kb plasmid has been cloned into the high-copy-number vector pUC19 and the restriction map of the resulting recombinant plasmid pRJ180 has been determined. Using sub-cloning and transposon mutagenesis, the klebicin B structural gene, the klebicin B immunity gene and the mitomycin C (MC) sensitivity gene () present on pRJ180 have been localized. Transposon inserts which inactivated klebicin production also abolished lysis protein production encoded by pRJ180, but did not affect klebicin B immunity. Using SDS-PAGE an MC-induced polypeptide of 85 kDa was observed in cultures of UNF5023(pRJ180). This polypeptide was absent in cultures carrying plasmid pRJ180 with a Tn insert which inactivated klebicin production. Analysis of the polypeptides present in the medium of JM83 (pRJ180) or UNF5023(pRJ180) indicated that the 85 kDa polypeptide is specifically secreted from the producing cell. Klebicin B has been purified, using gel filtration, from a cell-free extract of UNF5023(pRJ180) which had been induced with MC. After boiling in sample buffer the purified klebicin B gave rise to two peptides on SDS-PAGE, one of 85 kDa and the other of 11 kDa. Klebicin B-resistant mutants of UNF5023 were sensitive to klebicin A, colicin B and colicin D.


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