Synthesis of long, representative DNA copies of the murine RNA tumor virus genome.

Virions of Moloney murine leukemia virus can synthesize two classes of DNA molecules complementary to their 70S RNA. One class consists of molecules about 200 nucleotides long, which are of limited sequence complexity; these molecules are formed preferentially if the dNTP concentration during the reaction is low. The second class consists of very heterogeneous DNA molecules with weight-average size of about 1,000 nucleotides containing at least 70% of the viral RNA sequences in approximately equal concentration. The longest of these molecules can be 5,000 nucleotides long. This second class of DNA is formed in large amounts only in reactions containing dNTP concentrations of 0.2 mM or higher. In such reactions after 24 h of incubation, at least 35% of the input RNA is represented in DNA copies. The ability to make long, representative DNA transcripts of tumor virus RNA provides a source of excellent probes for molecular hybridization.