Identification of the bacteriophage Mu kil gene

The kil gene encoded in bacteriophage Mu DNA was previously shown to reside between the end of the B gene at 4.3 kb and the EcoRI site at 5.1 kb from the left end. To precisely map the kil gene within this region, two series of BAL-31 deletion derivatives were created: one removed Mu DNA rightward from the Hpal site (4.2 kb) and the other removed Mu DNA leftward from the EcoRI site. The deleted Mu DNA was subcloned into the expression vector pUC19 under lac promoter control and tested for the expression of the killing function following IPTG induction. Using DNA sequencing analysis, the Mu DNA in Kil+ and Kil- clones was precisely determined, and the kil gene was mapped to the first open reading frame beyond the B gene. The expression of the kil gene was sufficient to induce dramatic morphological changes: cells became enlarged and predominantly spherical, reminiscent of the phenotype of certain cell mutants.