In-vitro inhibition of RNA-instructed DNA polymerase.

Rifamycins and distamycins were assayed in vitro for their effects on the activity of a reverse transcriptase derived from the plasma of a patient with breast cancer. The inhibitory effect observed was compared with that of a human placental substance with a molecular weight of approximately 10 000. The latter substance is apparently also capable of affecting reverse transcriptase activity in vitro.