Abrogation of Fv-1b restriction with murine leukemia viruses inactivated by heat or by gamma irradiation.

Fv-1b restriction in BALB/3T3 cells is temporarily abrogated following infection with N-tropic murine leukemia virus. The mechanism of this phenomenon was investigated by comparing the inactivation rates for viral infectivity and for the ability of the same virus to abrogate Fv-1 restriction. Inactivation of the abrogating ability of N-tropic murine leukemia virus following graduated doses of gamma radiation proceeded at half the rate of that for viral infectivity. This result indicates that viral RNA must function in abrogating Fv-1b restriction but that only a portion of the viral genome is required. The inactivation kinetics of N-tropic murine leukemia virus were also determined following incubation of virus at 43 degrees C. Abrogating ability of N-tropic murine leukemia virus was found to be about six times as stable under these conditions as was viral infectivity. Interestingly, virion-associated reverse transcriptase activity was inactivated at the same rate as was viral infectivity, indicating that this enzyme may not need to function during abrogation. Virus heated at 43 degrees C was used to study the kinetics of the abrogation phenomenon itself. Abrogation was shown to be transient, requiring 6 to 9 h after virus infection to become maximally effective and beginning to disappear after about 18 h. The data reported here confirm the idea that abrogation of Fv-1 restriction can be separated experimentally from virus replication, and they raise the possibility that a separate biochemical pathway exists for incoming viral RNA in Fv-1 restrictive cells.