SPECIFICITY OF PRP24 BINDING TO RNA - A ROLE FOR PRP24 IN THE DYNAMICINTERACTION OF U4 AND U6 SNRNAS

Prp24 was previously isolated as a suppressor of a cold-sensitive U4 m utation and is required for at least the first step of splicing in vit ro. Our investigation of the in vitro RNA binding properties of the pu rified Prp24 protein shows that it binds preferentially to the U4/U6 h ybrid snRNAs compared to other snRNAs. The interaction between Prp24 a nd the U4/U6 hybrid appears to involve two regions in the RNA: the 39- 57 region of U6 and stem II of the U4/U6 hybrid. Interestingly, some U 4 mutations, which destabilize stem II, increase the affinity of Prp24 for the U4/U6 RNAs compared to the wild type. This suggests that the binding of Prp24 to the U4/U6 RNAs may involve some destabilization of the RNA duplex. We also found that Prp24 can stimulate the annealing of U4 and U6, suggesting that Prp24 participates in both the formation and disassembly of the U4/U6 hybrid during splicing.