A molecular link between SR protein dephosphorylation and mRNA export

Area of Science:

• Molecular Biology
• Cell Biology
• Gene Expression

Background:

• Multiple RNA-binding proteins, including serine/arginine-rich (SR) splicing factors, serve as adapters for mRNA nuclear export.
• These adapters interact with the export receptor TAP/nuclear export factor 1 (NXF1) to facilitate mRNA transport.
• Regulation of adapter-TAP interactions remains poorly understood.

Purpose of the Study:

• To investigate the regulation of interactions between SR protein adapters and the TAP/NXF1 export receptor.
• To determine how the phosphorylation state of SR proteins influences their binding affinity to TAP/NXF1.
• To elucidate the role of SR protein phosphorylation in the selectivity of mRNA export.

Main Methods:

• In vivo and in vitro splicing assays to monitor SR protein phosphorylation.
• Biochemical assays to measure the binding affinity of SR proteins to TAP/NXF1.
• Analysis of SR protein recruitment to pre-mRNA and spliced mRNA.

Main Results:

• SR proteins 9G8 and ASF/SF2 show increased affinity for TAP/NXF1 when hypophosphorylated.
• The SR protein 9G8 is recruited to pre-mRNA in a hyperphosphorylated state and becomes hypophosphorylated during splicing.
• TAP/NXF1 preferentially binds to spliced mRNA-protein complexes over pre-mRNA-protein complexes.

Conclusions:

• The phosphorylation state of SR protein adapters is a key regulatory mechanism for mRNA export.
• Hypophosphorylation of SR proteins enhances their interaction with TAP/NXF1, promoting efficient export of spliced mRNA.
• This phosphorylation-dependent mechanism contributes to the selectivity of TAP-mediated mRNA export.