FIGURE 4.
U25 binds equivalently to h15.5K and GST-15.5K. (A) Uniformly [32P]-uridine-labeled U25 binds h15.5K (closed triangles) with an apparent Kd = 73 ± 9 nM in a gel mobility shift assay. Wild-type U25, produced by ligating box C (open circles) or box D (open squares) oligonucleotides, binds GST-15.5K in a filter binding assay with affinities of 42 ± 3 nM or 70 ± 7 nM, respectively. (B) GST-15.5K binds wild type (circles, Kd = 35.9 ± 2.0 nM) and A9dA (triangles, Kd = 57 ± 3 nM) RNAs equivalently in the filter-binding assay. A9Pur (squares, Kd > 330 ± 30 nM) and A5dA (diamonds, Kd > 4200 ± 500 nM) RNAs exhibit substantially weaker binding.