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. Author manuscript; available in PMC: 2024 Jul 20.
Published in final edited form as: Mol Cell. 2023 Jul 3;83(14):2578–2594.e9. doi: 10.1016/j.molcel.2023.06.003

Figure 7. Model for SUGP1-DHX15 and proofreading at early spliceosome assembly.

Figure 7.

Left panel: On weak splice sites the transition from E complex to A complex is inhibited as PB binds to the U2 snRNP and prevents the full binding of the branch helix and recognition of the BP-A. These stalled spliceosomes are recognized by SUGP1-DHX15 and are discarded. Less mRNA is being produced in this scenario and more alternatively spliced mRNAs result.

Right panel: Mutation in SUGP1 weakens SUGP1 interaction with DHX15, removing the proofreading & discard pathway, allowing more time to assemble A complex and to proceed with splicing.