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Chick embryo cells transformed by Rous sarcoma virus (RSV) continue to synthesize 40--50 percent of control amounts of RNA following 12--24 hour exposure to 2 microng/ml of the toxin whereas normal chick embryo cells similarly treated synthesize less than 5 percent of control amounts of RNA. Analysis of cells treated with alpha-amanitin, or the resistant forms I and III polymerase, do not increase in infected cells over the levels found in uninfected control cells during the first 24 hours following infection indicating that increase in polymerase levels in infected cells does not account for the observed resistance. No significant difference was detected in the sensitivity to alpha-amanitin in the form II polymerase isolated from normal and transformed cells; The greater sensitivity of normal cells to alpha-amanitin can be reduced by growing the cells at low cell density but the resistance of RSV transformed cells is not significantly altered by changes in cell density. The results suggest that the resistance of RSV transformed cells may be related to altered control of density dependent contact-inhibition of the transformed cells.

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