UTILIZATION OF NONHOMOLOGOUS MINUS-STRAND DNA TRANSFER TO GENERATE RECOMBINANT RETROVIRUSES

During reverse transcription, minus-strand DNA transfer connects the s equences located at the two ends of the viral RNA to generate a long t erminal repeat. It is thought that the homology in the repeat (R) regi ons located at the two ends of the viral RNA sequences facilitate minu s-strand DNA transfer. In this report, the effects of diminished R-reg ion homology on DNA synthesis and virus titer were examined. A retrovi rus vector, PY31, was constructed to contain the 5' and 3' cis-acting elements from Moloney murine sarcoma virus and spleen necrosis virus. These two viruses are genetically distinct, and the two R regions cont ain little homology. In one round of replication, the PY31 titer was a pproximately 3,000-fold lower than that of a control vector with highl y homologous R regions. The molecular characteristics of the junctions of minus-strand DNA transfer were analyzed in both unintegrated DNA a nd integrated proviruses. Short stretches of homology were found at th e transfer junctions and were likely to be used to facilitate minus-st rand DNA transfer. Both minus-strand strong-stop DNA and weak-stop DNA were observed to mediate strand transfer. The ability of PY31 to comp lete reverse transcription indicates that minus-strand DNA transfer ca n be used to join sequences from two different viruses to form recombi nant viruses. These results suggest the provocative possibility that g enetically distinct viruses can interact through this mechanism.