Psr1 phosphatase regulates pre-mRNA splicing through spliceosomal B complex factor Snu66

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Precursor messenger RNA (pre-mRNA) splicing is a critical process for gene expression, regulated by modifications to spliceosomal components.
• Small nuclear RNAs (snRNAs) and spliceosomal proteins are key regulators of splicing fidelity and alternative splicing.
• The protein phosphatase Psr1 was previously known for its role in general stress response and plasma membrane localization in Saccharomyces cerevisiae.

Purpose of the Study:

• To investigate the potential regulatory role of the protein phosphatase Psr1 in pre-mRNA splicing.
• To determine if Psr1 interacts with and modifies core splicing factors.
• To elucidate the mechanism by which Psr1 influences splicing, particularly concerning non-canonical splice sites.

Main Methods:

• Investigated the interaction between Psr1 and the splicing factor Snu66 using biochemical assays.
• Assessed the dephosphorylation activity of Psr1 on Snu66.
• Utilized yeast deletion mutants (Psr1 deletion) and catalytically inactive mutants (tethered mutant) to study splicing defects.
• Examined the effect of Hub1 on the Psr1-Snu66 interaction.

Main Results:

• Psr1 binds and dephosphorylates the core splicing factor Snu66, independent of its plasma membrane localization.
• Psr1 is not an integral component of the spliceosome.
• Deletion of Psr1 or tethering of a catalytic mutant to Snu66 caused splicing defects, especially for introns with non-canonical 5' splice sites.
• Hub1 was found to displace Psr1 from Snu66, indicating a competitive interaction.

Conclusions:

• The protein phosphatase Psr1 plays a novel regulatory role in pre-mRNA splicing.
• Psr1 modulates Snu66 function through dephosphorylation, influencing the splicing of specific intron types.
• The interaction between Psr1, Snu66, and Hub1 highlights a complex regulatory network within the spliceosome.