Naïve balance between structural stability and DNA-binding ability of c-Myb R2R3 under physiological ionic conditions.

The minimum functional unit of c-Myb for specific DNA binding, c-Myb R2R3, fluctuates largely in solution which is critical for its DNA-binding function. The thermal stability of R2R3 increases with increasing NaCl concentrations and upon DNA binding as well. The DNA-binding affinity of R2R3 is stringently dependent on NaCl concentration, and decreases both with an increase or decrease in NaCl concentration from the physiological levels. The decreased DNA-binding affinity under low NaCl concentrations is because of the unfavorable entropy change, in contrast to the thermodynamic contribution under high NaCl concentrations. Together with the findings from thermal stability and structure analyses, the results indicate that R2R3 fluctuates more largely under low ionic strength than high ionic strength, resulting in its decreased stability and DNA-binding affinity. Under physiological conditions, R2R3 fluctuates properly to express its DNA-binding ability. The present results clearly show the naïve balance between structural stability and DNA binding.