DOWNSTREAM REGULATORY ELEMENTS INCREASE ACUTE AND LATENT HERPES-SIMPLEX VIRUS TYPE-2 LATENCY-ASSOCIATED TRANSCRIPT EXPRESSION BUT DO NOT INFLUENCE RECURRENCE PHENOTYPE OR ESTABLISHMENT OF LATENCY

The role of putative promoter or activator sequences downstream of the herpes simplex virus ape 2 latency-associated transcript (LAT) promot er and upstream of the LAT intron was investigated in vivo by construc ting and evaluating mutant viruses with deletions in this region. The deletion of LAT promoter sequences upstream of the primary LAT transcr ipt reduced levels of LAT expression during productive infections, com pared with the LAT expression level of wild-type virus, and abolished LAT expression during latency. The deletion of the putative downstream regulatory elements reduced but did not eliminate LAT expression duri ng productive and latent infections. The deletion of both regions almo st completely eliminated acute LAT transcription, although additional acute LAT-region transcription directed by sequences upstream of eithe r region was detected by reverse transcriptase PCR. The deletion of th e downstream elements did not influence the ability of the virus to re activate from latently infected guinea pigs relative to the ability of the wild-type virus to reactivate; thus, decreased LAT expression did not affect the frequency of recurrence. The deletion of both regions did not affect the ability of the virus to establish latency. We concl ude that downstream regulatory elements are necessary for maximal acut e LAT expression but do not constitute an independent promoter during latency and do not play an obvious role in the establishment of or rea ctivation from latency.