Characterization of the BcLF1 promoter in Epstein-Barr virus

This study characterizes the promoter region of the BcLF1 gene, which encodes viral capsid antigen in Epstein-Barr virus (EBV). Using primer extension analysis, researchers identified the transcription start site at nucleotide 137676 of the EBV genome. Through deletion analysis and luciferase reporter assays in P3HR1 cells, they determined that a critical 23 base-pair regulatory region between nucleotides -38 and -16 upstream of the start site is essential for BcLF1 transcription. This minimal region contains only a TATA sequence and no recognized transcription factor binding sites. The promoter is activated during lytic infection by phorbol ester treatment but repressed by phosphonoacetic acid, an inhibitor of viral DNA polymerase. Additionally, the study demonstrated that the oriLyt sequence (origin of lytic replication) significantly enhances BcLF1 expression when present in cis, increasing activity 17- to 40-fold. The findings suggest that BcLF1 transcription may require either removal of a negative regulator or expression of a positive factor specific to the lytic cycle, possibly involving a mechanism similar to herpes simplex virus late gene regulation.

Key findings

• The BcLF1 transcription start site is located at nucleotide 137676 of the EBV genome, confirmed by primer extension analysis.
• A minimal 23 bp promoter region (-38 to -16) containing only a TATA sequence is necessary and sufficient for BcLF1 regulation.
• The BcLF1 promoter is activated by phorbol esters during viral lytic cycle but repressed by DNA polymerase inhibitors like phosphonoacetic acid.
• The oriLyt sequence enhances BcLF1 expression 17- to 40-fold when present in cis, demonstrating that lytic DNA replication significantly boosts gene expression.