A plasmid-based rescue system [27] was used to generate a Gdeleted VSV driving expression of firefly luciferase and eGFP. The previously described genomic plasmid pVSV*DG(HA) containing 6 distinct transcription units (N-P-M-HA-eGFP-L) [28] was modified by replacing the influenza virus HA gene in the fourth position with eGFP taking advantage of MluI and BstEII endonuclease restriction sites upstream and downstream of the HA ORF, respectively. The firefly luciferase gene was amplified from the pBI-L plasmid (Clontech) by Pfu PCR and inserted into the fifth transcrition unit using XhoI and NheI endonuclease restriction sites. The resulting plasmid was designated pVSV*DG(Luc) and contained 6 genes in the order N-P-M-eGFP-Luc-L (Fig. 1) .