**5. Functional profiling of VZV genome**

Even though VZV has the smallest genome among all human herpesviruses, less than 20% of the VZV genome had been functionally characterized (Cohen et al, 2007). In order to investigate VZV ORF function, we created an entire library of single VZV ORF deletion mutants using the DY380 *E. coli* recombination system. The individual functions of each ORF were determined by transfecting MeWo cells with mutant DNA, and observing the subsequent growth of viral plaques. If a VZV ORF is nonessential for viral replication, plaques corresponding to the deleted ORF should be detectable 3-5 days after transfection and resemble the growth of the wild-type virus. Plaques that grow significantly smaller and later suggest that the ORF strongly influences optimal growth. The absence of a plaque entirely implies that the ORF is essential for viral replication.
