RNA-Dependent Synthesis of DNA by Virions of Mouse Leukemia Virus

A number of observations over the last seven years have led certain investigators to postulate that cells infected by RNA tumor viruses contain a DNA transcript of the viral genome (see Green, 1970). The recent discovery of an RNA polymerase in the virions of vesicular stomatitis virus (Baltimore, Huang, and Stampfer, 1970), which is an enveloped, single-stranded RNA virus, led us to ask whether the RNA tumor viruses, which also have an enveloped, single-stranded RNA genome, might contain an RNA-dependent DNA polymerase. Such an activity is demonstrable as will be documented below (Baltimore, 1970; Temin and Mizutani, 1970).