Identification of a varicella-zoster virus origin of DNA replication and its activation by herpes simplex virus type 1 gene products.

We have identified and characterized an origin of DNA replication in the genome of the human herpesvirus, varicella-zoster virus (VZV). This origin of replication (VZV ORIS) is located within the major inverted repeats in a position equivalent to that occupied by one of the herpes simplex virus type 1 (HSV-1) replication origins. Products encoded by both VZV and HSV-1 activate cloned copies of VZV ORIs, generating high molecular weight molecules consisting of tandem duplications of the input plasmid. The VZV ORIS region contains a tract of alternating A and T residues located at the centre of symmetry of an almost perfect palindrome of 45 bp, and the use of plasmid deletion mutants has demonstrated that this tract is an important functional element of the origin. Two sequences common to the VZV ORIS region and the regions specifying the two HSV-1 origins (ORIS, located within the TRS/IRS regions, and ORIL, located within the UL region) were identified and these may represent important recognition sites. One is an 11 bp sequence (CGTTCGCACTT), and the other is represented by the tract of alternating A and T residues. VZV does not appear to contain an origin of replication in a position equivalent to that of HSV-1 ORIL.