Mode of Action
Trimethoprim inhibits folate metabolism. Addition of folate to the medium can counteract trimethoprim.
Dihydrofolate Reductase (DHFR) is the gene counteracting trimethoprim.
Epicentre provides a Tn5 transposon system containing the DHFR gene for random knockouts of genes in bacteria.
Working concentrations and stock solutions
Working concentrations are typically 10 μg/ml. Trimethoprim is essentially insoluble, and very difficult to use as a stock solution. Addition of the powder is the easiest approach.