U6 snRNA function in nuclear pre-mRNA splicing: a phosphorothioate interference analysis of the U6 phosphate backbone

Area of Science:

• Molecular Biology
• RNA Biology
• Biochemistry

Background:

• U6 small nuclear RNA (snRNA) is crucial for pre-mRNA splicing catalysis.
• While nucleotide roles are known, the U6 phosphate backbone's function remains less understood.
• A previously identified nematode U6 snRNA mutation allows its use as a splicing substrate, enabling modification interference analysis.

Purpose of the Study:

• To identify essential pro-R oxygens in the U6 snRNA phosphate backbone for catalytic steps of splicing.
• To elucidate the specific roles of these oxygens in the first and second catalytic steps.
• To compare U6 snRNA's functional elements with group II introns.

Main Methods:

• Phosphorothioate substitution was used to probe the U6 snRNA phosphate backbone.
• Modification interference analysis was applied to U6 snRNA within the spliceosome.
• Mutational analysis and comparison with group II intron structures informed the study.

Main Results:

• Four pro-R oxygens are important for the first catalytic step of splicing; two are strictly required.
• One additional pro-R oxygen is uniquely essential for the second catalytic step.
• Key pro-R oxygens are located in the U2/U6 interaction region (helix 1b) and U6's intramolecular stem-loop.

Conclusions:

• Specific pro-R oxygens in the U6 snRNA backbone are critical for spliceosome catalysis.
• The identified essential oxygens highlight distinct roles in the first and second splicing steps.
• Functional similarities may exist between U6 snRNA and domain V of group II introns regarding catalysis.