Figure 4. Mtr4 associates with tri-snRNP proteins Prp3 and Prp4. (A) Coimmunoprecipitation reveals interaction of Mtr4 with Prp3. Antibodies against several Prp proteins and decay factors were used for IP from RNase-treated HeLa nuclear extract followed by western blot analysis. (B) Prp4 associates with Mtr4 in a similar IP conducted using anti-Mtr4 and probing the precipitate with anti-Prp4. Lane 4 is from the same gel as lanes 1–3, with the same exposure time. (C) U6 and U2 snRNAs were analyzed using quantitative RT PCR of Mtr4 IPs performed without RNase treatment. Results are presented as an average of two experiments.