Mutations in U6 snRNA that alter splice site specificity: implications for the active site

Area of Science:

• Molecular Biology
• RNA Biology
• Genetics

Background:

• Messenger RNA (mRNA) splicing involves precise cleavage events at specific sites.
• Mutations at the 5' splice site in Saccharomyces cerevisiae can lead to aberrant cleavage, posing a challenge to understanding splice site selection.

Purpose of the Study:

• To investigate the role of a base-pairing interaction between the 5' splice site and the U6 small nuclear RNA (snRNA) in determining 5' splice site choice.
• To test the hypothesis that this RNA-RNA interaction is a key determinant of accurate mRNA splicing.

Main Methods:

• A genetic approach was employed using Saccharomyces cerevisiae.
• Mutagenesis was performed on U6 snRNA and intron sequences to alter the predicted base-pairing interaction.
• The effects of these mutations on cleavage site selection were analyzed.

Main Results:

• Mutations predicted to stabilize the U6-intron interaction suppressed aberrant cleavage and enhanced normal cleavage at the 5' splice site.
• Stabilizing mutations restored accurate splicing even when the 3' splice site dinucleotide was mutated.
• These findings support a model where RNA-RNA interactions within the spliceosome are crucial for splice site fidelity.

Conclusions:

• A base-pairing interaction between the 5' splice site and the invariant ACAGAG sequence of U6 snRNA is a critical determinant of 5' splice site selection during mRNA splicing.
• This interaction contributes to the accuracy of the spliceosomal active site.
• The study provides insights into the complex RNA-RNA interactions governing the splicing process.