Splicing: HACking into the unfolded-protein response

Area of Science:

• Molecular Biology
• Cellular Biology
• Biochemistry

Background:

• Endoplasmic reticulum (ER) stress response is crucial for cellular health.
• Unfolded proteins in the ER activate specific signaling pathways.
• The Hac1p transcription factor regulates the unfolded protein response (UPR) in yeast.

Purpose of the Study:

• To investigate the molecular mechanism of RNA splicing triggered by unfolded proteins.
• To identify the key components involved in this specialized splicing event.
• To characterize the enzymatic activities of Ire1p and tRNA ligase in this process.

Main Methods:

• In vitro reconstitution assays using purified Ire1p and tRNA ligase.
• Site-specific RNA cleavage and ligation experiments.
• Analysis of RNA splicing products.

Main Results:

• Ire1p, a transmembrane kinase, possesses site-specific RNase activity.
• tRNA ligase is essential for joining the spliced RNA fragments.
• The combined action of Ire1p and tRNA ligase reconstitutes the Hac1p mRNA splicing.

Conclusions:

• The specialized RNA splicing of Hac1p mRNA is mediated by the RNase activity of Ire1p.
• tRNA ligase plays a critical role in completing the splicing process.
• This mechanism allows for the regulated translation of the Hac1p transcription factor during ER stress.