Competition for the conserved branch point sequence influences physiological outcomes in pre-mRNA splicing

Area of Science:

• Molecular Biology
• Genetics
• RNA Biology

Background:

• Spliceosome assembly involves recognizing intron branch points, influencing mRNA structure and levels.
• The branch point sequence motif (UACUAAC) is conserved, but multiple proteins can recognize it in some species.

Purpose of the Study:

• To investigate the competition between SF1 and Quaking (QKI) for specific intron branch sites (ACUAA) in mammalian cells.
• To elucidate the mechanism by which QKI influences alternative splicing and its functional consequences.

Main Methods:

• Utilized mutant reporter assays derived from introns with dual branch site-like sequences.
• Investigated protein binding and spliceosome factor recruitment using QKI occupancy at dual branch sites.
• Examined the effects of ectopic QKI expression in budding yeast.

Main Results:

• SF1 activates exon inclusion, while QKI represses it at ACUAA branch sites.
• QKI binding at dual branch sites prevents SF1 binding and spliceosome factor recruitment.
• Ectopic QKI expression in yeast leads to lethality due to widespread splicing repression.

Conclusions:

• QKI acts as a splicing repressor by competing with SF1/BBP for a subset of branch point sequences.
• QKI's high-affinity binding to specific branch sites underlies its repressive function.
• QKI plays a critical role in regulating splicing, with potential implications for cellular viability.