Relative quantification of vTR RNA in infected CEC. CEC were mock infected (MI) or infected with either the parental virus vRB-1B, the mutant virus vPchTR^+/+, the rescuant virus vPvTR^+/+ or a virus deleted for both vTR copies (vCR1-4^−/−). At 48 h p.i., total RNA was extracted and used for qRT-PCR analysis of vTR expression. Relative expression of vTR gene was normalized to cellular GAPDH expression levels. Error bars represent standard error of the mean of two independent experiments at the 48 h time point.