DIFFERENCES IN WATER RELEASE FOR THE BINDING OF ECORI TO SPECIFIC ANDNONSPECIFIC DNA-SEQUENCES

The free energy difference between complexes of the restriction nuclea se EcoRI with nonspecific DNA and with the enzyme's recognition sequen ce is linearly dependent on the water chemical potential of the soluti on, set using several very different solutes, ranging from glycine and glycerol to triethylene glycol and sucrose. This osmotic dependence i ndicates that the nonspecific complex sequesters some 110 eaters more than the specific complex with the recognition sequence. The insensiti vity of the difference in number of waters released to the solute iden tity further indicates that this water is sequestered in a space that is sterically inaccessible to solutes, most likely at the protein-DNA interface of the nonspecific complex. Calculations based on the struct ure of the specific complex suggest that the apposing DNA and protein surfaces in the nonspecific complex retain approximately a full hydrat ion layer of water.