Abstract
The DNA polymerase enzymes from avian, murine, and feline RNA tumor viruses can be distinguished by their ability to read specific, synthetic primertemplates. The copying of templates containing adenylic and thymidylic acids by all these DNA polymerases is inhibited by ethidium bromide, though this compound affects the polymerases from mammalian tumor viruses much more than the enzyme from avian tumor viruses. Conversely, ethidium bromide stimulates the ability of the enzymes from avian tumor viruses to use primertemplates containing only guanylic and cytidylic acids, whereas the mammalian tumor virus enzymes are moderately inhibited.