Construction of a fol mutant strain of Escherichia coli for use in dihydrofolate reductase mutagenesis experiments.

A strain of Escherichia coli with the fol gene deleted and a kan gene inserted in its place was created for use in cloning and isolation of mutant dihydrofolate reductase. Southern blot analysis and dihydrofolate reductase enzyme assays confirmed the delta fol::kan genotype. A thyA mutation accompanied the fol deletion and is required for survival of a dihydrofolate reductase-deficient strain.