Conditionally lethal genes in the N pilus region of plasmid pCU1

Plasmid genes or regions that are conditionally lethal to Escherichia coli have been called kil and those lethal to Klebsiella but not to E. coli have been called kik. Both classes of genes are found in or close to the N pilu s region of the plasmid pCU1 and the closely related plasmid pKM101. Here w e describe two new and overlapping lethal genes that are located between ki kA and traA of the plasmid pCU1 and display host specificity. KilC is letha l in E. coli and Klebsiella while kikC is lethal only in Klebsiella. The pr eviously identified korA gene is sufficient to override the lethality of ki lC in trans or in cia but is insufficient to override kikC. kilC expression in E. coli leads to cell death accompanied by an increase in average cell length without affecting septum formation. (C) 1999 Academic Press.