The assembly and post-splicing reassembly of the U4/U6.U5 tri-snRNP remain to be investigated. We report here that ZIP， a protein containing a CCCH-type zinc finger and a G-patch domain， as characterized by us previously， regulates pre-mRNA splicing independent of RNA binding. We found that ZIP physically associates with the U4/U6.U5 tri-small nuclear ribonucleoprotein (tri-snRNP). Remarkably， the ZIP-containing tri-snRNP， which has a sedimentation coefficient of ～35S， is a tri-snRNP that has not been described previously. We also found that the 35S tri-snRNP contains hPrp24， indicative of a state in which the U4/U6 di-snRNP is integrating with the U5 snRNP. We found that the 35S tri-snRNP is e... More
The assembly and post-splicing reassembly of the U4/U6.U5 tri-snRNP remain to be investigated. We report here that ZIP， a protein containing a CCCH-type zinc finger and a G-patch domain， as characterized by us previously， regulates pre-mRNA splicing independent of RNA binding. We found that ZIP physically associates with the U4/U6.U5 tri-small nuclear ribonucleoprotein (tri-snRNP). Remarkably， the ZIP-containing tri-snRNP， which has a sedimentation coefficient of ～35S， is a tri-snRNP that has not been described previously. We also found that the 35S tri-snRNP contains hPrp24， indicative of a state in which the U4/U6 di-snRNP is integrating with the U5 snRNP. We found that the 35S tri-snRNP is enriched in the Cajal body， indicating that it is an assembly intermediate during 25S tri-snRNP maturation. We showed that the 35S tri-snRNP also contains hPrp43， in which ATPase/RNA helicase activities are stimulated by ZIP. Our study identified， for the first time， a tri-snRNP intermediate， shedding new light on the assembly and recycling of the U4/U6.U5 tri-snRNP.
