Cover. Graphical representation of a double mutant cycle involving the U1A-U1 snRNA complex reported by Tuite et al. in this issue [Nucleic Acids Res. (2002) 30, 5269--5275]. The stick figure in each frame shows the wild-type structure. The top panel represents the substitution of the non-polar base isostere 4-methylindole for adenine, the bottom panel represents the substitution of Leu for Phe, and the right panel illustrates the complex containing both substitutions. Leu and 4-methylindole are shown with transparent space-filling models superimposed upon the wild-type structure. Mutation of Phe to Leu results in a large loss of binding affinity that is partially recovered by the substitution of 4-methylindole for adenine.
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