Genetic analysis of ColN plasmid determinants for colicin production, release, and immunity

Colicin N was identified as the 39,000-molecular-weight protein encoded by the 4,900-base-pair, multiple copy number, amplifiable plasmid ColN -284. Its production was controlled by the SOS regulatory circuit and by catabolite repression. Colicin accumulated intracellularly to ca. 10(6) molecules per cell after growth for 2 to 3 h in medium containing 0.5 microgram of mitomycin C per ml and was then released as the cells underwent partial lysis. Strains carrying pColN -284 and its derivatives exhibited low-level immunity to colicin N and were fully sensitive to all other colicins tested. Regions of the plasmid responsible for colicin N activity (cna), for mitomycin-induced lysis ( cnl ), and for colicin N immunity ( cni ) were localized and characterized by cloning, transposon Tn5 and hydroxylamine mutagenesis, and restriction endonuclease deletion and mapping analysis. The results are discussed in terms of both the organization of the cna, cnl , and cni genes and the respective role of cnl expression and colicin N production in mitomycin sensitivity, colicin export, and induced partial lysis of ColN + cells.