The equid herpesvirus-1 gene 63 is expressed as a leaky late (γ 1) transcript and is nonessential for replication in vitro

The regulation of Equid herpesvirus-1 (EHV-1) gene 63 was investigated using molecular expression studies and its role in viral growth was identified by constructing a gene 63 mutant virus. Metabolic inhibitors were used to show that EHV-1 gene 63 is expressed as a leaky-late (γ 1) transcript. Transient transfections and subsequent chloramphenicol acetyltransferase (CAT) reporter assays showed that gene 63 was transactivated by EHV-1 gene 64 (immediate early) protein. An EHV-1 gene 63 mutant virus, where the LacZ gene was inserted into the mutated gene 63 open reading frame, showed that gene 63 protein was not essential for efficient EHV-1 growth in tissue culture. These findings indicate that the animal αherpesviruses may have evolved different pathways leading to replication.