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The impact of Prp18p on splicing fidelity and efficiency in budding yeast

ABSTRACT: Fidelity of 3´-splice site (3´SS) selection by the spliceosome is critical for proper gene expression but is a daunting task considering the low complexity of the 3´SS consensus YAG. Here we show that loss of the splicing factor Prp18p in budding yeast activates a diverse array of alternative 3´SS at more than half of all introns. Some alternative sites highly diverge from the YAG consensus, demonstrating a critical role for Prp18p in promoting spliceosome fidelity. Usage of alternative 3´SS is determined by distance from the branchpoint, local RNA secondary structures, upstream poly(U) content, and adenosine enrichment in exons. The 3´SS fidelity function of Prp18p can be genetically uncoupled from its role in splicing efficiency and is promoted by interactions with Slu7p and Prp8p. Taken together, these results provide a comprehensive mechanism into how the spliceosome achieves specificity of 3´SS selection and how it prevents aberrant activation of non-canonical splice sites.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE131797 | GEO | 2020/05/25

REPOSITORIES: GEO

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Project description:The spliceosome undergoes extensive rearrangements as it assembles in multiple steps onto the precursor messenger RNA. In the earliest assembly step, U1snRNA identifies the 5' splice site through base-pairing interactions. However, U1snRNA leaves the spliceosome relatively early in the assembly process. The 5' splice site identity is subsequently maintained through interactions with U6snRNA, protein factor PRP8, and other components of the spliceosome during the complex assembly and rearrangements that build the catalytic site. Using a forward genetic screen in C. elegans, we have identified splicing suppressors of a locomotion defect caused by a 5'ss mutation. Here we report three new extragenic suppressor alleles from this screen, two in PRP8 and one in SNRNP200/Brr2. mRNASeq studies of these suppressor strains indicates that there are specific native targets with alternative 5' and alternative 3' splicing events affected by these suppressors, especially for the suppressor PRP8 D 1549N (position D1556 in humans). The strong suppressor at the unstructured N-terminus of SNRP200, N18K, indicates a potential regulatory role for this region. By examining distinct changes in the splicing of native genes, and by mapping these conserved suppressor residues onto cryoEM structural models of assembling human spliceosomes, we conclude that there are multiple interactions in the spliceosome that are required to ensure that the initial 5'ss identified by U1snRNA early in spliceosome assembly is the one that gets loaded into the catalytic core.The spliceosome undergoes extensive rearrangements as it assembles in multiple steps onto the precursor messenger RNA. In the earliest assembly step, U1snRNA identifies the 5' splice site through base-pairing interactions. However, U1snRNA leaves the spliceosome relatively early in the assembly process. The 5' splice site identity is subsequently maintained through interactions with U6snRNA, protein factor PRP8, and other components of the spliceosome during the complex assembly and rearrangements that build the catalytic site. Using a forward genetic screen in C. elegans, we have identified splicing suppressors of a locomotion defect caused by a 5'ss mutation. Here we report three new extragenic suppressor alleles from this screen, two in PRP8 and one in SNRNP200/Brr2. mRNASeq studies of these suppressor strains indicates that there are specific native targets with alternative 5' and alternative 3' splicing events affected by these suppressors, especially for the suppressor PRP8 D 1549N (position D1556 in humans). The strong suppressor at the unstructured N-terminus of SNRP200, N18K, indicates a potential regulatory role for this region. By examining distinct changes in the splicing of native genes, and by mapping these conserved suppressor residues onto cryoEM structural models of assembling human spliceosomes, we conclude that there are multiple interactions in the spliceosome that are required to ensure that the initial 5'ss identified by U1snRNA early in spliceosome assembly is the one that gets loaded into the catalytic core.

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The impact of Prp18p on splicing fidelity and efficiency in budding yeast

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