Regulation of eukaryotic gene expression is achieved at different levels, which require accurate coordination. Macromolecular assemblies that exist as pre-formed entities can account for such coordination. Processing of pre-mRNA represents one step in this cascade of regulatory events but, moreover, provides explanation for protein versatility. The cellular machine where splicing of pre-mRNA, as well as additional processing events, take place in vivo is termed the supraspliceosome. Here, we show that the supraspliceosome is composed of four active spliceosomes, termed native spliceosomes, connected to each other by the pre-mRNA. Cleavage of pre-mRNA shows that its integrity is essential for the stability of the supraspliceosome. Furthermore, supraspliceosomes can be reconstituted in vitro, from purified native spliceosomes by addition of synthetic pre-mRNAs, providing further support to the supraspliceosome as a preassembled biological complex. The internal setting of the native spliceosomes within the supraspliceosome is most suitable to enable the communication between these structures, which is crucial in order to achieve regulated splicing.
Bibliographical noteFunding Information:
We thank A. Pecho for technical assistance, C. Wachtel for the CDP construct, I. Sela for the tobacco mosaic virus and G. Sasson for drawing the model. This research was funded, in part, by grants from The Volkgwagen Foundation and the Israel-US Binational Science Foundation (R. S.) and the Helen and Milton Kimmelman Center for Biomolecular Structure and Assembly at the Weizmann Institute of Science (J. S.).
- Eukaryotic pre-mRNA
- RNA polymerase II