Arginine methylation of Sam68 and SLM proteins negatively regulates their poly(U) RNA binding activity

Area of Science:

• Molecular Biology
• Biochemistry
• RNA Biology

Background:

• Sam68 and its homologs (SLM-1, SLM-2) are RNA-binding proteins containing arginine-glycine (RG) repeats.
• Protein arginine methyltransferase 1 (PRMT1) methylates arginine residues within these RG repeats.
• The impact of this arginine methylation on RNA binding remains largely unknown.

Purpose of the Study:

• To investigate whether arginine methylation affects the RNA binding capabilities of Sam68 and SLM proteins.
• To determine the role of RG repeats in the RNA binding of these proteins and how methylation influences it.

Main Methods:

• In vitro poly(U) binding assays using purified proteins and peptides.
• Cellular overexpression of PRMT1 to induce methylation.
• Assessment of RNA binding ability in cells following PRMT1 overexpression.

Main Results:

• Arginine methylation of Sam68 and SLM proteins markedly reduced their poly(U) binding ability in vitro.
• The RG repeats of Sam68 bind poly(U), but methylation abrogated this binding.
• Overexpression of PRMT1 increased Sam68 and SLM methylation in cells, decreasing their poly(U) binding.

Conclusions:

• The RG repeats in Sam68 and SLM proteins may act as auxiliary RNA binding domains.
• Arginine methylation by PRMT1 can eliminate or significantly reduce the RNA binding ability of Sam68 and SLM proteins.
• This suggests a regulatory mechanism for RNA binding through post-translational modification.