A mutational analysis of U12-dependent splice site dinucleotides

Area of Science:

• Molecular Biology
• RNA Splicing
• Genetics

Background:

• The U12-dependent minor spliceosome is responsible for splicing a subset of introns in humans.
• These introns are classified into /AU-AC/ and /GU-AG/ groups based on their splice site dinucleotides.
• Understanding the rules governing these splice sites is crucial for comprehending gene expression regulation.

Purpose of the Study:

• To investigate the in vivo and in vitro splicing phenotypes of mutations in U12-dependent intron splice site dinucleotides.
• To determine the impact of specific nucleotide substitutions on the efficiency of minor intron splicing.
• To explore potential communication between the 5' and 3' splice sites and the role of branch site distance.

Main Methods:

• Site-directed mutagenesis of 5' and 3' splice site dinucleotides in U12-dependent introns.
• In vivo and in vitro splicing assays to assess the functional impact of mutations.
• Analysis of splicing efficiency across different sequence combinations and branch site distances.

Main Results:

• Specific 5' and 3' splice site dinucleotide combinations significantly influence splicing efficiency.
• A 5' A residue shows broad compatibility, while 5' G prefers G or U at the 3' site.
• 5' U or C residues are largely deleterious, and communication between splice sites was not observed in double mutants.

Conclusions:

• The identity of nucleotides at the 5' and 3' splice sites critically dictates U12-dependent intron splicing.
• Evidence suggests communication between the first and last nucleotides of the intron, influencing 3' splice site activity.
• Optimal branch site to 3' splice site distance is conserved across both /GU-AG/ and /AU-AC/ intron classes.