Controlled by disorder: Phosphorylation modulates SRSF1 domain availability for spliceosome assembly

Area of Science:

• Molecular Biology
• Biochemistry
• RNA Biology

Background:

• Serine/arginine-rich splicing factor 1 (SRSF1) is crucial for mRNA processing, including transcription, splicing, and nuclear export.
• Dysfunctional SRSF1 is implicated in various diseases, including cancers and developmental disorders.
• SRSF1's function depends on interactions with proteins and RNA, regulated by phosphorylation of its arginine/serine-rich (RS) tail.

Purpose of the Study:

• To investigate how phosphorylation of the SRSF1 RS tail affects its protein and RNA interactions.
• To elucidate the impact of phosphorylation on SRSF1's phase separation properties.
• To understand the role of SRSF1 phosphorylation in early spliceosome assembly.

Main Methods:

• Nuclear Magnetic Resonance (NMR) paramagnetic relaxation enhancement (rE)
• NMR chemical shift perturbation (CSP)
• Analysis of protein-RNA interactions and phase separation

Main Results:

• Unphosphorylated SRSF1's RS tail interacts with the RRM1 protein-binding site.
• Phosphorylation of RS reduces interaction with the RRM1 protein-binding site but increases interaction with the RRM1 RNA-binding site.
• Phosphorylation weakens SRSF1's RNA binding and alters its phase separation by reducing arginine's role in intermolecular interactions.

Conclusions:

• Phosphorylation dynamically regulates SRSF1's intramolecular interactions, influencing its protein and RNA binding affinities.
• Altered SRSF1 interactions due to phosphorylation impact its phase separation behavior.
• These findings offer insights into SRSF1's role in spliceosome assembly and its regulation.