Summary of Recent Observations on the Molecular Biology of RNA Tumor Viruses and Attempts at Application to Human Leukemia

Abstract

RNA tumor viruses apparently replicate through a DNA intermediate (provirus), a reaction catalyzed by the polymerase of these viruses, the so-called “reverse transcriptase.” The viral genomic RNA is large (about 70S) and contains large tracts of poly A. These viruses can be induced by some halogenated pyrimidines from some non-producer cells. The induction of these viruses can be blocked by 3′-deoxyadenosine (cordycepin) but only at a very specific time (12 to 18 hours after induction). The mechanism of this block in induction may be due to interference with normal processing of the viral RNA after its transcription from proviral DNA, perhaps by blocking poly A formation. A reverse transcriptase is present in cytoplasmic particulate fractions from some patients with acute leukemia. This enzyme is very similar to the reverse transcriptase of viruses and may be viral in origin. Some criteria for its detection and features which distinguish it from major DNA polymerases of cells are reviewed. Some rationales and approaches for inhibition of viral replication are discussed.