In vitro transcriptional activation, dimerization, and DNA-binding specificity of the Epstein-Barr virus Zta protein

The Epstein-Barr virus BZLF1 immediate-early gene encodes a transcriptional activator protein, Zta, which acts as a key regulatory switch in the transition between the latent and lytic viral life cycle. In this work, full-length Zta was expressed at high levels in Escherichia coli and purified to homogeneity by DNA affinity chromatography. The bacterial protein bound to specific target sequences (Zta response elements) and activated transcription in vitro from an Epstein-Barr virus early target promoter (BHLF1). Zta bound to DNA as a dimer. The formation of a heterodimer with a Zta deletion mutant was detected by gel electrophoresis mobility shift assays. Footprinting analysis on the BHLF1, BZLF1, and simian virus 40 control regions revealed multiple binding sites with no simple consensus sequence. Zta bound upstream from its own promoter at low concentrations, while at high concentrations it bound at the transcription start site, suggesting that it may activate and then autoregulate its own expression. These results demonstrate that Zta is a sequence-specific DNA-binding transcription factor.