The EHV-1 UL4 protein that tempers viral gene expression interacts with cellular transcription factors

- The UL4 gene is conserved in the genome of DI particles of EHV-1.
- The UL4 gene is not essential for EHV-1 lytic replication.
- The UL4 protein binds to cellular transcription factors TBP and Pol II.
- Late viral gene expression is enhanced in UL4 null virus infection.
- Viral DNA synthesis is not retarded in cells infected with the UL4-null virus.

The UL4 gene is conserved within the genome of defective interfering particles of equine herpesvirus type 1 (EHV-1) that mediate persistent infection. Here, we show that the UL4 protein inhibits EHV-1 reporter gene expression by decreasing the level of transcribed mRNA. The UL4 protein did not bind any gene class of EHV-1 promoters in electromobility or chromatin immunoprecipitation assays, but directly interacted with the TATA box-binding protein (TBP) and the carboxy-terminal domain of RNA polymerase II both in vitro (GST-pulldown assays) and in infected cells (coimmunoprecipitation analyses). Microarray analyses of the expression of the 78 EHV-1 genes revealed that viral late genes important for virion assembly displayed enhanced expression in cells infected with UL4-null virus as compared to wild-type or UL4-restored EHV-1. Quantitative PCR analyses showed that viral DNA replication was not retarded in cells infected with the UL4-null virus as compared to wild-type EHV-1.