DNA sequences which regulate the expression of the pseudorabies virus major immediate early gene

It has been shown previously that the transcription of herpes simplex virus (HSV) immediate early (IE) genes is transactivated by a component of the virus particle. The trans-inducing factor (TIF) is known to be polypeptide Vmw65. Infection with pseudorabies virus (PRV), a related herpesvirus, does not increase expression from HSV IE regulatory sequences (W. Batterson and B. Roizman, 1983, J. Virol. 46, 371-377). To examine the control of the PRV IE gene and possible sequence specificity of a TIF, the 5' terminus of the PRV major IE transcript was mapped and hybrid plasmids containing PRV upstream sequences linked to the HSV-1 TK gene were constructed. Gene expression under the control of PRV IE or HSV-1 IE gene 3 upstream regions were compared using transient expression assays. It was found that infection with uv-irradiated PRV did not stimulate expression from PRV IE or from HSV-1 IE gene 3 upstream regions, indicating that PRV did not possess an effective TIF. Infection with uv-treated HSV-1, or cotransfection with a plasmid which encodes Vmw65, stimulated expression from both PRV and HSV IE gene upstream regions. The nucleotide sequence of the 5' end of the PRV transcript and its upstream region was determined. This region was, in overall structure, unlike the upstream regions of HSV IE genes but showed a strong similarity to the enhancers of human and murine cytomegaloviruses (HCMV and MCMV). In particular, a reiterated 15-bp element of the PRV upstream region was homologous to a conserved, repeated sequence element found in both HCMV and MCMV enhancer regions and was also related to the "TAATGARATTC" motif found upstream of all HSV IE genes. Thus a conserved sequence element occurs upstream of IE genes in four herpesviruses with different genome structures and diverse biological properties.