RESUMO
The spliceosome is assembled through a step-wise process of binding and release of its components to and from the pre-mRNA. The remodeling process is facilitated by eight DExD/H-box RNA helicases, some of which have also been implicated in splicing fidelity control. In this study, we unveil a contrasting role for the prototypic splicing proofreader, Prp16, in promoting the utilization of aberrant 5' splice sites and mutated branchpoints. Prp16 is not essential for the branching reaction in wild-type pre-mRNA. However, when a mutation is present at the 5' splice site or if Cwc24 is absent, Prp16 facilitates the reaction and encourages aberrant 5' splice site usage independently of ATP. Prp16 also promotes the utilization of mutated branchpoints while preventing the use of nearby cryptic branch sites. Our study demonstrates that Prp16 can either enhance or impede the utilization of faulty splice sites by stabilizing or destabilizing interactions with other splicing components. Thus, Prp16 exerts dual roles in 5' splice site and branch site selection, via ATP-dependent and ATP-independent activities. Furthermore, we provide evidence that these functions of Prp16 are mediated through the step-one factor Cwc25.
The DExD/H-box protein Prp16 has a well-established role in proofreading the 5' splice site and the branch site of precursor mRNA through ATP hydrolysis to ensure the accuracy of the splicing process. Our research has unveiled an unexpected facet of Prp16's function, as it also promotes aberrant selection of the 5' splice site and the branch site through an ATP-independent activity. Prp16 accomplishes these contrasting functions by interacting with the step-one factor Cwc25. It can stabilize Cwc25 to enhance the branching reaction independently of ATP, or destabilize Cwc25 to inhibit the reaction through its ATPase activity. Prp16 exerts dual roles in splice site selection, employing ATP-dependent and ATP-independent mechanisms to regulate splicing fidelity.
Assuntos
Precursores de RNA , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae , Adenosina Trifosfatases/genética , Adenosina Trifosfatases/metabolismo , Trifosfato de Adenosina/metabolismo , RNA Helicases/genética , RNA Helicases/metabolismo , Precursores de RNA/genética , Precursores de RNA/metabolismo , Sítios de Splice de RNA , Splicing de RNA , Fatores de Processamento de RNA/genética , Fatores de Processamento de RNA/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Spliceossomos/genética , Spliceossomos/metabolismoRESUMO
Splicing of pre-mRNA is initiated by binding of U1 to the 5' splice site and of Msl5-Mud2 heterodimer to the branch site (BS). Subsequent binding of U2 displaces Msl5-Mud2 from the BS to form the prespliceosome, a step governing branchpoint selection and hence 3' splice site choice, and linking splicing to myelodysplasia and many cancers in human. Two DEAD-box proteins, Prp5 and Sub2, are required for this step, but neither is stably associated with the pre-mRNA during the reaction. Using BS-mutated ACT1 pre-mRNA, we previously identified a splicing intermediate complex, FIC, which contains U2 and Prp5, but cannot bind the tri-snRNP. We show here that Msl5 remains associated with the upstream cryptic branch site (CBS) in the FIC, with U2 binding a few bases downstream of the BS. U2 mutants that restore U2-BS base pairing enable dissociation of Prp5 and allows splicing to proceed. The CBS is required for splicing rescue by compensatory U2 mutants, and for formation of FIC, demonstrating a role for Msl5 in directing U2 to the BS, and of U2-BS base pairing for release of Prp5 and Msl5-Mud2 to form the prespliceosome. Our results provide insights into how the prespliceosome may form in normal splicing reaction.