Equine herpesvirus 1 gene expression is governed by the interactions of viral regulatory proteins and cellular transcription factors

Equine herpesvirus 1, a member of the Alphaherpesvirinae subfamily, is investigated as a model of alphaherpesvirus gene regulation, pathogenesis, and persistent infection mediated by defective interfering particles. The focus of the research presented in this dissertation was to begin to elucidate the regulatory functions of the EICP27 protein by determining if this protein interacts with the IE protein, and whether these two EHV-1 regulatory proteins associate with cellular transcription factors. The IE gene is essential for virus replication because it encodes a protein that is the major trans-activator of viral promoters and is responsible for the commencement of viral gene expression. The experimental data presented in this dissertation demonstrate a direct physical interaction between the IE protein and the cellular transcription factor TFIIB, and identify the domains within these regulatory proteins that mediate this interaction. The EICP27 gene is expressed early in infection as a 470-amino acid protein that cooperates in a synergistic manner with the IE protein in the trans-activation of EHV-1 promoters. Evidence from this study indicates that the contributions of the EICP27 protein to the viral gene program are not mediated by an acidic trans-activation domain, as this EHV-1 protein lacks this motif that is capable of independently stimulating transcription. However, the EICP27 protein was shown to interact directly with the cellular transcription factor TATA box-binding protein, and the domain within the EICP27 protein that mediates this interaction was identified. In addition, the EICP27 protein was shown to interact physically with the IE protein. The EICP27 protein-binding domain within the IE protein was mapped to a region that is involved in the interactions of the IE protein with viral promoters, the EHV-1 EICP0 protein, and cellular TFIIB. The EICP27 protein does not directly bind to viral promoter sequences; however, one consequence of the EICP27-IE protein interaction is the recruitment of the EICP27 protein to viral promoter complexes, the assembly of which is initiated by the IE protein. Collectively, these initial findings expand our understanding of the role of the EICP27 regulatory protein in the regulated expression of EHV-1 genes.