Unusual properties of AKR MCF-247 murine leukemia virus unintegrated proviral DNA

Analyses of Hirt extracts from endogeneous murine leukemia virus (MuLV)-infected cells revealed the presence of 9-kbp linear DNA and two superhelical forms with one or two tandem copies of the long terminal repeat (LTR). In contrast, cells that were infected with AKR MCF247 MuLV yielded two major linear forms of 9.0 and 8.4 kbp and one discrete superhelical DNA. In addition, there was a heterogeneous population of superhelical DNAs that were larger and smaller than the major superhelical DNA species. Restriction endonuclease treatment of purified linear and superhelical DNAs have revealed that MCF247 MuLV unintegrated viral DNA is very heterogeneous. Evidence is presented that there are at least two linear DNAs; one is 9-kbp full-length linear DNA, whereas the other major form contains a 0.6 to 0.7-kbp deletion in the envelope gene adjacent to the right LTR. In addition, there are two size classes of the LTR in at least the full-length linear DNA. The major superhelical DNA species is a 8.4-kbp form which contains one copy of the LTR. Other heterogeneous superhelical DNAs appear to contain env-gene deletions or partially deleted copies of a tandem LTR region.