Functional characterization of the equine herpesvirus type 1 immediate-early gene product

The genes of equine herpesvirus type 1 (EHV-1) are coordinately-expressed and temporally-regulated in an immediate-early (IE), early (E), and late (L) fashion. Biochemical evidence indicates that expression of the EHV-1 IE gene is essential to the initiation of E and L gene expression. To investigate the role of the IE gene product in the induction of E and L gene expression, transient transfection assays were performed in which L-M cells were cotransfected with an EHV-1 IE gene expression vector and various EHV-1 promoter-chloramphenicol acetyl-transferase (CAT) reporter constructs representative of the three temporal classes of EHV-1 genes. It was determined that: (i) the IE gene product inhibits gene expression directed by its own promoter, (ii) cis-acting IE promoter sequences conferring autoregulatory activity map between coordinates ;The EHV-1 IE gene product is a proline- and alanine-rich polypeptide of 1487 amino acids. Mutational analysis of the IE gene product indicated that: (i) a domain mapping within the first 322 amino acid residues of the IE polypeptide is essential for trans-activation activity, (ii) residues 322 to 421 contain a domain conferring IE autoregulatory activity, and (iii) a C-terminal domain spanning residues 951 to 1487 contains the nuclear localization signal of the IE polypeptide, as well as an additional domain that contributes to trans-activation activity.