Predicted structural similarities of the DNA binding domains of c-Myc and endonuclease Eco RI.

The c-Myc oncoprotein belongs to a family of proteins whose DNA binding domains contain a basic region-helix-loop-helix (bHLH) motif. Systematic mutagenesis of c-Myc revealed that dimerized bHLH motifs formed a parallel four-helix bundle with the amino termini of helices 1 and 2 directed toward the inner and outer nucleotides of the DNA binding site, respectively. Both the basic region and the carboxyl-terminal end of the loop contributed to DNA binding specificity. The DNA binding domain of c-Myc may therefore be structurally similar to that of restriction endonuclease Eco RI.