The herpesviral terminase complex is part of the intricate machinery that delivers a single viral genome into empty preformed capsids (encapsidation). The varicella-zoster virus (VZV) terminase components (pORF25, pORF30, and pORF45/42) have not been studied as extensively as those of herpes simplex virus 1 and human cytomegalovirus (HCMV). In this study, VZV bacterial artificial chromosomes (BACs) were generated with small (⌬30S), medium (⌬30M), and large (⌬30L) ORF30 internal deletions. In addition, we isolated recombinant viruses with specific alanine substitutions in the putative zinc finger motif (30-ZF3A) or in a conserved region (region IX) with predicted structural similarity to the human topoisomerase I core subdomains I and II ( During herpesvirus replication, large head-to-tail doublestranded DNA (dsDNA) concatemers accumulate in the infected-cell nucleus and are subsequently packaged into preformed viral capsids. The packaging process is complex and involves a group of proteins that recognize specific viral DNA sequences and simultaneously process and translocate unit-length genomes through the portal vertex of the procapsid (1). The protein complex that docks or interacts with the capsid portal protein consists of the heterotrimeric viral terminase. Terminases of DNA bacteriophages have been well described (2, 3), and those of several members of the Herpesviridae, including herpes simplex virus 1 (HSV-1) (4-14), human cytomegalovirus (HCMV) (15-21), Epstein-Barr virus (EBV) (22), and varicella-zoster virus (VZV) (23)(24)(25), are under investigation.Members of the Alphaherpesvirinae, Betaherpesvirinae, and Gammaherpesvirinae share a core set of orthologous proteins required for DNA encapsidation. A heterotrimeric viral terminase complex consisting of three of these conserved core proteins was recently isolated from HSV-1-infected cells (4). The HSV-1 terminase consisted of a 1:1:1 equimolar complex of two different terminase protein subunits, pUL15 and pUL28, and a protein encoded by the UL33 gene family. The pUL33 component may act as an essential accessory protein involved in the formation and/or stability of the terminase complex (7). Homologous terminase components have also been identified for HCMV (pUL89, pUL56, and pUL51) (16)(17)(18)(19)(20)(21)(26)(27)(28) and VZV (pORF45/42, pORF30, and