FIG. 2.

Construction of cnf1 mutants. Plasmid pSE297 containing a 1.4-kb internal fragment of cnf1 on a suicide vector was introduced into E. coli F3 and F11 by electroporation and selection for the tetracycline resistance of the vector. The resulting, mutated cnf1 locus contains two truncated cnf1 genes flanking the integrated vector. Integration of pSE297 sequences at the chromosomal cnf1 locus was confirmed by amplifying fragments from the junctions between the integrated vector and cnf1 sequences (see Materials and Methods).