DISTINCT DNA-BINDING PREFERENCES FOR THE C-MYC MAX AND MAX MAX DIMERS

The transcription factor c-Myc and its dimerisation partner Max are me mbers of the basic/helix-loop-helix/leucine-zipper (bHLH-Z) family and bind to the DNA core sequence CACGTG. Using a site-selection protocol , we determined the complete 12 base pair consensus binding sites of c -Myc/Max (RACCACGTGGTY) and Max/Max (RANCACGTGNTY) dimers. We find tha t the c-Myc/Max dimer fails to bind the core when it is flanked by a 5 'T or a 3'A, while the Max/Max dimer readily binds such sequences. Fur thermore we show that inappropriate flanking sequences preclude transa ctivation by c-Myc in vivo. In conclusion, Max/Max dimers are less dis criminatory than c-Myc/Max and may regulate other genes in addition to c-Myc/Max targets.