SR proteins function in coupling RNAP II transcription to pre-mRNA splicing

Area of Science:

• Molecular Biology
• Gene Expression Regulation
• RNA Processing

Background:

• Transcription and splicing are functionally linked processes in eukaryotes.
• The precise molecular mechanisms governing this transcription-splicing coupling remain largely unknown.
• Efficient splicing of RNA polymerase II (RNAP II) transcripts is crucial for gene expression.

Purpose of the Study:

• To identify proteins that mediate the functional coupling between transcription and splicing.
• To elucidate the mechanism by which transcription influences RNA splicing.
• To understand how splicing factors are recruited to nascent RNAP II transcripts.

Main Methods:

• Comprehensive proteomic analysis of immunopurified human RNA polymerase II.
• Identification and characterization of specifically associated proteins.
• Functional assays to assess the role of identified factors in transcription-splicing coupling.

Main Results:

• Over 100 proteins specifically associated with human RNAP II were identified.
• SR proteins and all U1 small nuclear ribonucleoprotein (snRNP) components were found to be associated with RNAP II.
• SR proteins were shown to function in coupling transcription to splicing via cotranscriptional recruitment.

Conclusions:

• SR proteins and U1 snRNP are key factors in coupling transcription and splicing.
• Cotranscriptional recruitment of SR proteins to RNAP II transcripts facilitates efficient spliceosome assembly.
• This mechanism ensures early access of splicing factors to nascent pre-mRNA, outcompeting inhibitory proteins.