WATER RELEASE ASSOCIATED WITH SPECIFIC BINDING OF GAL REPRESSOR

Water release coupled to the association of gal repressor with DNA is measured from the sensitivity of the binding constant to the solution osmotic pressure, using neutral solutes that are typically excluded fr om polar protein and DNA surfaces. Differences in water release for bi nding of repressor to different sequences are linked with differences in specificity and binding energies. With sucrose, the specific bindin g of repressor to operator sequences is accompanied by the release of 130 water molecules. No water release is seen for the weak, non-specif ic binding of repressor to poly(dI-dC).(dI-dC). A difference in the re lease of six water molecules is seen even for the binding of gal repre ssor to two different operator sequences that differ in affinity by on ly a factor of two.