The proto-oncogene c-myc (myc) encodes a transcription factor (Myc) that promotes growth, proliferation and apoptosis. Myc has been suggested to induce these effects by induction/repression of downstream genes. Here we report the identification of potential Myc target genes in a human B cell line that grows and proliferates depending on conditional myc expression. Oligonucleotide microarrays were applied to identify downstream genes of Myc at the level of cytoplasmic mRNA. In addition, we identified potential Myc target genes in nuclear run-on experiments by changes in their transcription rate. The identified genes belong to gene classes whose products are involved in amino acid/protein synthesis, lipid metabolism, protein turnover/folding, nucleotide/DNA synthesis, transport, nucleolus function/RNA binding, transcription and splicing, oxidative stress and signal transduction. The identified targets support our current view that myc acts as a master gene for growth control and increases transcription of a large variety of genes.

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The Epstein‐Barr virus protein EBNA2 acts as a transcriptional activator of cellular and viral genes and plays a crucial role in the immortalization of human primary B‐cells by EBV. We have shown previously that EBNA2 transactivates the promoters of the latent membrane antigens LMP, TP1 and TP2. The promoter of the TP1 gene was chosen as a model system to study the molecular mechanism of EBNA2 mediated transactivation. To identify an EBNA2 dependent cis‐acting element, various TP1 promoter‐reporter gene constructs were transfected in the absence and presence of an EBNA2 expression vector into the established B‐cell line BL41‐P3HR1. We were able to delineate an 81 bp EBNA2 responsive region between −258 and −177 relative to the TP1 RNA start site. The element worked in either orientation and could mediate EBNA2 dependent transactivation on a heterologous promoter. Electrophoretic mobility shift assays revealed three specific protein‐DNA complexes formed with sequences of the EBNA2 responsive element. Two of these were not cell type specific, but the third was detected only in EBNA2 positive cell extracts. Gel‐shift analysis in the presence of EBNA2 specific monoclonal antibodies revealed that EBNA2 is a component of the third complex. Thus, these experiments demonstrate that EBNA2 interacts with an EBNA2 responsive cis‐element of the TP1 promoter.

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