ROLE OF CIS-ACTING SEQUENCES OF THE ICPO PROMOTER OF HERPES-SIMPLEX VIRUS TYPE-1 IN VIRAL PATHOGENESIS, LATENCY AND REACTIVATION

A mutant herpes simplex virus type 1, termed Delta Tfi, with a 350 bp deletion of the Sp1, NF-kappa B, TAATGARATs, C/EBP and F2 DNA-binding elements from -420 to -70 relative to the transcriptional start site o f ICPO (Vmw 110), was generated and characterized, The efficiency of p lating of Delta Tfi was reduced on Vero cells and it expressed correct ly initiated ICPO RNA in the presence of cycloheximide, although RNA l evels were 2 . 5-fold lower than with wild-type (KOS) and marker-rescu ed (Delta TfiR) viruses, This was consistent with a demonstrated reduc tion in ICPO protein expression for Delta Tfi at early times post-infe ction and a 3-fold reduction in ICPO-dependent transactivation of the ICP6 promoter, KOS, Delta Tfi and Delta TfiR replication in murine cor neas and trigeminal ganglia were comparable when measured on a complem enting cell line, but Delta Tfi titres appeared 15- to 50-fold lower w hen measured on Vero cells, Delta Tfi was correspondingly less virulen t than wild-type or marker-rescued viruses in both immunocompetent and SCID mice. Delta Tfi, however, established and reactivated from laten cy with efficiencies comparable to wild-type and marker-rescued viruse s, These results demonstrate that although this deletion of the ICPO p romoter results in lower levels of ICPO in vitro and decreased virulen ce in vivo, the establishment of and reactivation from latency are una ffected, This indicates that elements which regulate ICPO expression a nd virulence during acute infection may be distinct from those involve d in reactivation.