A role for U2/U6 helix Ib in 5' splice site selection

Area of Science:

• Molecular Biology
• RNA Biology
• Genetics

Background:

• Splice site selection is critical for accurate gene expression.
• U6 snRNA G52 influences the first intron nucleotide selection.
• U2 alleles can suppress U6-G52 mutations, suggesting U2 involvement.

Purpose of the Study:

• To investigate the role of U2 snRNA in 5' splice site selection.
• To determine if specific U2 snRNA regions interact with U6 snRNA in splice site selection.
• To elucidate the structural and functional significance of U2/U6 interactions.

Main Methods:

• Site-directed mutagenesis of U2 snRNA at position 23.
• Analysis of splice site cleavage accuracy in mutant strains.
• Assessment of synthetic lethality with U6-G52 mutations.
• Investigation of U2/U6 helix Ib structure restoration.

Main Results:

• U2 snRNA mutations at position U23, but not adjacent sites, specifically impair 5' splice site cleavage.
• All U2-U23 mutations exhibit synthetic lethality with a thermosensitive U6-G52U allele.
• A U2-U23C substitution results in hyperaccurate splicing, reducing cleavage of introns with a +1G substitution.
• Restoring the U2/U6 helix Ib structure suppresses splice site cleavage defects.

Conclusions:

• U2 snRNA position U23 is essential for accurate 5' splice site selection.
• The U2/U6 helix Ib structure plays a unique and critical role in splice site recognition.
• This function of helix Ib is distinct from that of U2/U6 helix II, challenging notions of redundancy.