Your laboratory has isolated a new strain of Zaire ebolavirus from a human blood sample collected in Liberia. You have determined that it causes non-lytic CPE and replicates to 10^7 pfu/ml in a human endothelial cell line. After passaging the virus 7 times in the cell line, CPE no longer occurs and the virus titer drops to 10^4 pfu. You are interested in determining why the virus has become attenuated and perform an experiment to screen dozens of drugs that disrupt various parts of the antiviral immune response of cells. Treatment of cells with one drug, fludarabine, restores the CPE in treated cells and the virus replicates to 2 times l0^6 pfu/ml. a. What protein is fludarabine’s cellular target and effect? b. Why is the attenuated virus able to cause CPE and replicate to high titer in treated cells? c. What viral gene is most likely mutated in the attenuated virus?