Characterization of a Molecular Clone of RFM/Un Mouse Chromosomal DNA that Contains a Full-length Endogenous Murine Leukaemia Virus-related Proviral Genome

SUMMARY A 12.4 kbp HindIII chromosomal DNA fragment harbouring an apparently intact 9-2 kbp endogenous marine teukaemia virus (MuLV)-related proviral genome was isolated from an RFM/Un strain mouse by molecular cloning and designated pRFM # 6. Nucleotide sequence analysis revealed the following characteristic features in the pRFM # 6 provirus: a distinct 200 bp sequence in the long terminal repeat (LTR) mid-U3 region, a primer binding site for glutamine tRNA, a 3' pol region encoding an 'endonuclease' protein of 390 amino acids, and the mink cell focus- forming virus type-specific sequence at the 5' portion of the env gene. The 699 bp 5' LTR and 700 bp 3' LTR of pRFM # 6 provirus were identical except for three base changes in the U3 'enhancer' region. At the cell-provirus DNA junction, 4 bp direct repeats were present. The proviral genome was found at the same chromosomal DNA site in BALB/c, AKR, C3H, CBA and RFM strain mice, but not in NFS/N or C57BL/6 strain mice.