The c-Myc oncoprotein (Myc) is a DNA sequence-specific transcription factor that 
regulates transcription of a wide variety of genes involved in the control of 
cell growth, proliferation, differentiation, and apoptosis and its deregulated 
expression is implicated in many types of human cancer. Myc has an N-terminal 
transcription activation domain (TAD) that interacts with various coactivators 
and a C-terminal basic-helix-loop-helix-leucine zipper (bHLHZip) domain required 
for E box-specific DNA-binding and heterodimerization with its obligatory 
bHLHZip protein partner Max. The analysis of the mechanisms by which the Myc:Max 
complex regulates transcription at the molecular level in vitro has been 
hampered by the difficulty in obtaining highly pure recombinant Myc:Max 
heterodimers that contain full-length Myc with its complete TAD domain and that 
have sequence-specific DNA-binding activity. Here, we describe a simple method 
to reconstitute recombinant Myc:Max complexes from highly purified full-length 
proteins expressed in Escherichia coli that are soluble and highly active in E 
box-specific DNA-binding in vitro. The reconstituted Myc:Max complexes are 
stable and lack Max:Max homodimers. This procedure should facilitate the 
characterization of the DNA-binding and transcription activation functions of 
full-length Myc:Max complexes in vitro and in particular the role of Myc 
TAD-interacting cofactors and Myc:Max post-translational modifications.