Three distinct elements within the murine c-myc promoter are required for transcription

We have undertaken a detailed analysis of the cis-acting elements that are required for optimal transcription initiation from P2, the major promoter of the murine c-myc gene. We find that three elements contribute to promoter strength, termed ME1a2, E2F and ME1a1 at positions -85, -64 and -46 respectively (relative to P2). Individually the elements are weak, but combined they contribute to full promoter activity, all acting in a positive fashion. The E2F element is the site at which the SV40 large T antigen transactivates the c-myc promoter. However, transactivation requires the presence of the ME1a2 or ME1a1 elements in addition to E2F. By a number of criteria it appears that the ME1a2 and ME1a1 elements bind the same or a very closely related protein (monomer Mr 94,000). It was found that Hela cells contain a novel factor that is capable of binding to the ME1a1 and ME1a2 elements but only in the presence of the protein-dissociating agents deoxycholate or formamide. Finally, the E2F factor binds DNA both as a monomer and as a multiprotein complex; the latter is cell type specific. Both types of bound E2F factor form less stable protein-DNA complexes than the ME1a2/ME1a1 factor.