We will continue to investigate the structural/functional features of herpes simplex virus type 1 genes important in their controlled expression during productive infection. We will use reporter plasmids capable of being activated by trans-acting viral product because of their convenience in the manipulation of specific sequence elements involved in regulation. Such methods will be used to precisely identify sequence elements in selected viral leaders that are responsive to trans-activation by viral gene products and to examine the role of template replication on the expression of genes of different temporal classes. Sequence elements identified as important in virus-specific activation and repression of transcription will be utilized as probes to investigate the nature of the interaction between viral control sequences and specific regulatory proteins expressed during viral replication. Selected sequences will be modified and reintroduced into the virus itself so that alterations in expression of marker genes during productive infection can be examined. We have characterized a single gene expressed as mRNA during latent infection and will now characterize the anti-ICPO gene in terms of its sequence, control of its expression, and the protein products encoded by it. Such information will be used to manipulate the expression of anti-ICO to investigate the molecular basis for the exclusive expression of this transcript in neurons and any role it may have in productive infection.