2′-O-Methyl oligoribonucleotides complementary to U1, U2, U5, and U6 snRNAs were added individually to HeLa nuclear extracts, and the splicing reactions were preincubated at 30 °C for 10 min. The concentration of individual 2′-O-methyl oligonucleotides was titrated to give partial inhibition of splicing (U1, 8 μM; U2, 0.3 μM; U5, 12 μM; U6, 13 μM) (17). TauEx10−11d5 WT and N279K mutant pre-mRNAs were then added, and the incubation was continued for 1.5 h. Splicing reaction products were analyzed by urea-polyacrylamide gel electrophoresis. Quantification of three independent experiments is shown in B, showing a consistent and significant increase in the ratio of N279K/WT splicing products as compared with mock-treated or U2, U5, or U6 oligonucleotide-treated reactions.