Replacement of the fip gene of Escherichia coli by an inactive gene cloned on a plasmid.

To determine whether the fip gene of Escherichia coli, which is required for filamentous phage assembly, is required for cell viability, we replaced the chromosomal copy of the gene with an inactive copy introduced on a plasmid. We found that the fip gene is dispensable. The method we devised, which should be generally useful, was also tested with an inactivated rho gene. As expected, the rho gene is essential.