The trans-activation of the UL31 promoter by a single or double effector vectors. Reporter plasmid [pUL31(-1033/-3)-Luc], and effector plasmids (pSVIE, pSVIR2, pCMV-IR4 (EICP22), pSVEICP0, pSVUL5 (EICP27), pCMV-ETIF, and pCMV-UL31) were used for promoter assays. Relative luciferase units (RLU). Error bars indicate the mean ± SD. (A) UL31 promoter activity by a single effector plasmid. (B) UL31 promoter activity by double effector plasmids.