The proto-oncogene c-myc governs the expression of a number of genes targeting 
cell growth and apoptosis, and its expression levels are distorted in many 
cancer forms. The current investigation presents an analysis by proteolysis, 
circular dichroism, fluorescence and Biacore of the folding and ligand-binding 
properties of the N-terminal transactivation domain (TAD) in the c-Myc protein. 
A c-Myc sub-region comprising residues 1-167 (Myc1-167) has been investigated 
that includes the unstructured c-Myc transactivation domain (TAD, residues 
1-143) together with a C-terminal segment, which appears to promote increased 
folding. Myc1-167 is partly helical, binds both to the target proteins Myc 
modulator-1 (MM-1) and TATA box-binding protein (TBP), and displays the 
characteristics of a molten globule. Limited proteolysis divides Myc1-167 in two 
halves, by cleaving in a predicted linker region between two hotspot mutation 
regions: Myc box I (MBI) and Myc box II (MBII). The N-terminal half (Myc1-88) is 
unfolded and does not alone bind to target proteins, whereas the C-terminal half 
(Myc92-167) has a partly helical fold and specifically binds both MM-1 and TBP. 
Although this might suggest a bipartite organization in the c-Myc TAD, none of 
the N and C-terminal fragments bind target protein with as high affinity as the 
entire Myc1-167, or display molten globule properties. Furthermore, merely 
linking the MBI with the C-terminal region, in Myc38-167, is not sufficient to 
achieve binding and folding properties as in Myc1-167. Thus, the entire N and 
C-terminal regions of c-Myc TAD act in concert to achieve high specificity and 
affinity to two structurally and functionally orthogonal target proteins, TBP 
and MM-1, possibly through a mechanism involving molten globule formation. This 
hints towards understanding how binding of a range of targets can be 
accomplished to a single transactivation domain.