While it has been known for some time that the c-Myc protein binds to random DNA sequences, no sequence-specific binding activity has been detected. At its carboxyl terminus, c-Myc contains a basic—helix-loop-helix (bHLH) motif, which is important for dimerization and specific DNA binding, as demonstrated for other bHLH protein family members. Of those studied, most bHLH proteins bind to sites that contain a CA- -TG consensus. In this study, the technique of selected and amplified binding-sequence (SAAB) imprinting was used to identify a DNA sequence that was recognized by c-Myc. A purified carboxyl-terminal fragment of human c-Myc that contained the bHLH domain bound in vitro in a sequence-specific manner to the sequence, CACGTG. These results suggest that some of the biological functions of Myc family proteins are accomplished by sequence-specific DNA binding that is mediated by the carboxyl-terminal region of the protein.

The myc family of proto-oncogenes encodes short-lived nuclear phosphoproteins (Myc) involved in the control of cell proliferation and differentiation. Here we discuss the evidence for Myc's involvement in normal and abnormal cell proliferation and review recent information on Max, a novel protein that forms a sequence-specific DNA-binding complex with Myc. The properties of the Myc: Max heterodimeric complex suggest a model for how Myc may function in the cell.

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