Specificity of hnRNP LL binding to ESS1 is consistent with a unique role in signal-induced exon repression. (A) Sequence of WT ESS1 with location and identity of mutations indicated. Underlined residues correspond to the ARS core motif repeats. (B) UV cross-linking and immunoprecipitation as done in Figure 4 for WT and mutant ESS1 RNAs. (C) RT–PCR analysis of minigenes with WT or indicated mutant ESS1 sequence inserted into ESS1 location of construct shown in Figure 5A. Minigenes were cotransfected with 1 or 3 μg of Flag-hnRNP LL, and quantitation of RT–PCR was as done for Figure 5. Overall exon skipping was somewhat lower in these experiments than in Figure 5 due to inherent variation in transient transfections, but data shown in each figure are from parallel experiments and are thus internally controlled.
