SUMMARY

NIH/3T 3 cells chronically infected with the Moloney strain of murine leukaemia virus were incubated with interferon (IF). There was no effect on virus production during the first 4 h, but thereafter an antiviral state gradually developed, reaching a maximum at about I2 h. When IF was removed, the antiviral state (expressed in terms of inhibition of release of virus) remained constant for IO h, after which there was an abrupt return to the normal rate of virus release. Analysis of IF-treated cells showed that there was a three to fourfold increase in the amount of virus RNA in the nucleus at 48 h after IF addition, and still a slight increase at 72 h. There were no increases in the amounts of virus RNA in the cytoplasm during 72 h after the addition of IF. These results agree with the postulate that IF inhibits a late stage in the maturation of virus in chronically infected cells