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. Author manuscript; available in PMC: 2014 Nov 18.
Published in final edited form as: Biochem Soc Trans. 2010 Aug;38(4):1110–1115. doi: 10.1042/BST0381110

Figure 1.

Figure 1

Complexes formed during spliceosome assembly and activation Intron containing pre-mRNAs with 5′SS (5′ splice site), BS (branch site) and 3′SS (3′ splice site) sequences are recognised by the spliceosomal snRNPs during spliceosome assembly and activation. The U1 and U2 snRNPs interact with the 5′SS and BS, respectively, to form complex A. The ATPase Prp28 then allows the U4/U6.U5 tri-snRNP to assemble with the pre-mRNA along with the NTC proteins to form complex B. The GTPase Snu114 and the ATPase Brr2 induce U4/U6 unwinding with subsequent destabilisation of the U1 and U4 snRNPs to form the complex BACT. The ATPase Prp2 then remodels the spliceosome to the complex B* which is the catalytically active spliceosome. The action of Cwc25 and Yju2 then induce step 1 of splicing and formation of complex C which contains the step 1 intermediates. Finally the ATPases Prp16 and Prp22 induce step 2 of splicing and formation of the post-splicing complex which contains the spliced mRNA and the removed intron. This post-splicing complex is then disassembled and the snRNPs and NTC proteins are recycled for another round of splicing.