Initiation of the Epstein-Barr virus (EBV) lytic cycle is dependent on expression of the viral transactivator Zta, which is encoded by the BZLF1 gene. Described here is an initial mapping of the regions of Zta involved in activating transcription. The data indicate that the amino-terminal 153 amino acids of Zta are important for activity, and in particular the region from residues 28 to 78 appears to be critical for Zta function. However, other features of Zta may be important for activity since a Gal4-Zta chimeric protein, generated by fusing the amino-terminal 167 residues of Zta to the DNA binding domain of the yeast transactivator Gal4, transactivated a minimal promoter containing one upstream Gal4 binding site but was unable to exhibit synergistic transactivation when assayed with a reporter containing five upstream Gal4 binding sites.