Characterization of –35 binding complexes using in-gel cross-linking. Following EMSA with p5424 nuclear extracts and labeled -35 probe, gel slices were exposed to UV radiation for 0, 15, 30, or 60 minutes, then exposed to film without drying. Individual complexes 1, 2, and 3 were then identified and extracted from the gel in denaturing/reducing loading buffer and were analyzed by SDS-PAGE. Approximate molecular weights are indicated.