Table 13. 2 Thermodynamic Effects of Mutations in the a Repressor on Operator Binding AG Relative to Wild-Type, kcal mol Mutant Wild-Type Interaction Operator△ G Nonoperator△G yr-22- Phe Backbone phosphate 1.6 GIn-33- Ser Backbone phosphate Asn-52-Asp Backbone phosphate 6.2 >2.8 Gly-43- Glu Backbone phosphate 6.2 0.5 GIn-44-Ser Hydrogen Bond to A(2)N7,-NH 3.7 0.2 GIn-44- Leu Hydrogen Bond to A(2)N7,NH >6.2 0.2 Ser-45- Leu Hydrogen Bond to G(4)N7 >6.2 0.1 Asn-55- Lys Hydrogen Bond to G(6)N7, Lys-4 Lys-4-GIn Hydrogen Bond to G(6)06, Asn-55 5.2 0.5 Ala-49- Val Hydrophobic T(3)-CH 4.6 0.2 Ala-49-+Asp Hydrophobic T(3)CH >6.2 0.1 66 >104 >103