Reverse Transcriptas

Recognition of RNA tumor viruses as causative agents of malignant disease started with the observation (by Ellerman and Bang in 1908) that a filterable agent transmitted avian leukemia1 and the subsequent isolation of chicken sarcoma virus by Rous in 1911.2 These findings were followed by an intense and continuous search for new isolates, the establishment of inbred strains of mice, and the development of tissue culture techniques. In the early 1960s, the significance of RNA tumor viruses was generally accepted, especially in avian and murine systems, but with some skepticism, probably because its role in natural disease was not yet evident. Moreover, the mode of replication of the RNA tumor viruses was still not understood. In recent years, the study of these viruses markedly intensified, principally because of a discovery which filled a major gap in the understanding of their replication. This is the independent discovery of the viral RNA-dependent DNA polymerase (reverse transcriptase) by Temin and Mizutani3 and by Baltimore4 in 1970. This discovery also extended our understanding of the mode of genetic information transfer, and it paved the way for the finding of viral-related components, reverse transcriptase5-11 and type-C viral related nucleic acids in human leukemic cells by Gallo, Spiegelman, and their co-workers (see later section10,12-17).