Mutations in U1 snRNA bypass the requirement for a cell type-specific RNA splicing factor

Area of Science:

• Molecular Biology
• Genetics
• RNA Splicing

Background:

• Efficient RNA splicing of the yeast MER2 gene is dependent on the MER1 protein, which is expressed during meiosis.
• The precise role of MER1 in MER2 splicing and the mechanisms governing this process remain incompletely understood.

Purpose of the Study:

• To identify genetic factors that can bypass the requirement for MER1 in MER2 RNA splicing.
• To elucidate the molecular mechanisms underlying MER1-independent MER2 splicing.

Main Methods:

• A genetic selection strategy was employed to isolate second-site mutations that suppress the MER1 dependency.
• Sequence analysis of suppressor mutations and analysis of RNA-DNA interactions were performed.

Main Results:

• A mutation in SNR19, encoding U1 small nuclear RNA (snRNA), was identified as a suppressor.
• This mutation alters the U1 snRNA sequence, enabling it to base pair with a site in the MER2 intron outside the canonical 5' splice site.
• Restoring the consensus sequence at the MER2 5' splice site also alleviated the MER1 requirement, correlating with increased U1 snRNA base pairing.

Conclusions:

• The MER1 protein's requirement for MER2 splicing can be bypassed by mutations affecting U1 snRNA interactions.
• This suggests that U1 snRNA can engage with non-canonical sites within introns to facilitate splicing under certain conditions.
• The findings provide new insights into the flexibility of splice site recognition and the regulation of meiotic gene splicing in yeast.