MULTIPROTEIN COMPLEX-FORMATION ON THE C-MYC PROMOTER

The E2F element is a cis-acting DNA sequence within the P2 promoter of the c-myc proto-oncogene. While it is required for optimal transcript ion, the multiprotein complexes formed on this site have not been well characterized. We show that in extracts of human glioblastoma cells a nd NIH3T3 fibroblasts, significant E2F transcription factor binding to the c-myc E2F site occurs as a both a monomer (the active form) and a s only two mutually exclusive complexes with the retinoblastoma gene p roduct (pRb) or the cyclin A protein. The E2F protein monomer was foun d predominantly in the cytosolic fraction of the cellular extracts whi le the pRb and cyclin A complexes in the nuclear fraction, indicating that the monomer has novel physical properties. Thus, protein complex formation on the c-myc E2F site appears to contribute in a unique way to transcriptional activation.