Exon mutations uncouple 5' splice site selection from U1 snRNA pairing

Area of Science:

• Molecular Biology
• Genetics
• RNA Splicing

Background:

• Yeast 5' splice junction mutations (GUAUGU) cause aberrant pre-mRNA cleavage.
• Previous studies identified cleavage near correct 5' splice sites.

Purpose of the Study:

• To investigate if exon mutations can convert aberrant cleavage sites into functional 5' splice sites.
• To determine the role of the conserved G at the 5' end of introns in splicing.
• To analyze the impact of exon mutations on U1 snRNA-pre-mRNA pairing and splice site selection.

Main Methods:

• Introduction of exon mutations into yeast pre-mRNA.
• In vivo and in vitro splicing assays.
• Analysis of aberrant mRNA translation.
• Assessment of U1 snRNA-pre-mRNA pairing.

Main Results:

• Exon mutations successfully converted aberrant cleavage sites into functional 5' splice sites.
• Aberrant mRNAs resulting from these mutations were translated in vivo.
• The conserved G at the intron 5' end is essential for the second step of splicing.
• Splice site selection occurred independently of U1 snRNA-pre-mRNA pairing, which remained unaffected by exon mutations.

Conclusions:

• Exon mutations can functionally rescue aberrant 5' splice sites in yeast.
• The conserved intronic G plays a critical role in the second splicing step.
• Precise 5' splice site selection is independent of U1 snRNA binding.