In some jurisdictions, a party who loses in a small-claims court is entitled to a trial "de novo" in a court of more general jurisdiction and with more formal procedures.
After fusion, the cells are grown in a medium with methotrexate or aminopterin that inhibit the enzyme dihydrofolate reductase thus blocking the de novo synthesis of thymidine monophosphate.
Despite the presence of the "de novo" pathway, the salvage reactions are essential in humans; a lack of niacin in the diet causes the vitamin deficiency disease pellagra.