In vitro synthesis and characterisation of full and half genome length complementary DNA from avian oncoviruses

RNA TUMOUR viruses carry an RNA-dependent DNA polymerase which can transcribe the viral RNA genome into single-stranded and double-stranded DNA in detergent-disrupted virions 1,2 . For several years since the discovery of this enzyme, only short DNA fragments of about 100–200 nucleotides long could be produced 3 . Recently, conditions have been described for the synthesis of possibly full-genome length complementary DNA (cDNA) 4–6 . The in vitro conditions described, however, were not well characterised and did not seem to be very efficient. We report here an efficient synthesis in vitro of half- and possibly full-genome length cDNA in avian oncoviruses. These two discrete species of cDNA were synthesised in large quantities. Furthermore, some of the half-genome length cDNA were found to form single-stranded circular molecules with a distinct secondary structure.