Transcription factor that binds DNA in a non-specific manner, yet also specifically recognizes the core sequence 5'-CAC[GA]TG-3'. Activates the transcription of growth-related genes. Efficient DNA binding requires dimerization with another bHLH protein. Binds DNA as a heterodimer with MAX (By similarity). C-MYC I is active in oocytes, while C-MYC II is active in both oocytes and post-gastrula embryos. The 9aaTAD motif is a transactivation domain present in a large number of yeast and animal transcription factors.