IDENTIFICATION OF A NEW INHIBITOR OF ESSENTIAL DIVISION GENE FTSZ AS THE KIL GENE OF DEFECTIVE PROPHAGE RAC

A gene function carried by a plasmid, causing arrest of cell division in Escherichia coli, has been identified as the product of a short ope n reading frame of the prophage Rac, previously designated orfE, expre ssed only under conditions of prophage induction. Because Rac carries a killing function expressed under conditions of zygotic induction, an orfE-defective Rac(+) strain was constructed. This strain had lost th e killing function, indicating that orfE is kil. Division inhibition b y kil was specifically relieved by overexpression of essential divisio n gene ftsZ. The kil gene product acts independently of the min operon , and its effects are increased in conditions of high cyclic AMP (cAMP ) receptor protein-cAMP complex levels in the cell. Furthermore, at hi gh levels of expression, kil product distorts the rod shape of the cel ls. These features distinguish kil-encoded protein from the inhibitory product of gene dicB, which occupies a similar genetic location in Ki m (Qin), another defective prophage of Escherichia coli.