Cloning of the Escherichia coli K-12 dihydrofolate reductase gene following mu-mediated transposition.

The dihydrofolate reductase structural gene, folA, has been closed into the multicopy vector pBR322 following the gene's enrichment by bacteriophage Mu-mediated transposition. Strains carrying the resultant plasmid, pJFM8, produce 25 to 30 times more dihydrofolate reductase than control strains. Consequently they are resistant to trimethoprim, an inhibitor of this enzyme. This elevation in enzyme production is due to an increase in the number of folA gene copies per cell. The higher yield of dihydrofolate reductase obtained will be extremely useful for purifying and characterising this trimethoprim-sensitive chromosomally derived enzyme. The plasmid will also be invaluable for studying the structure, function and regulation of dihydrofolate reductase.