Export of Discarded Splicing Intermediates Requires mRNA Export Factors and the Nuclear Basket

Core Concepts

The export of discarded splicing intermediates requires mRNA export factors Mex67p, Nab2p, Yra1p, and Nlp3, as well as the nuclear basket component Mlp1p. Tom1p-mediated ubiquitylation of Yra1p is crucial for efficient lariat intermediate export.

Abstract

The study investigates the mechanism behind the export of discarded splicing intermediates in budding yeast. It reveals that lariat intermediates utilize the same export machinery as mRNAs, requiring Mex67p and its adaptors Nab2p, Yra1p, and Nlp3. Surprisingly, Mlp1p promotes rather than hinders the export of lariat intermediates through its interaction with Nab2p. Additionally, Tom1p-mediated ubiquitylation of Yra1p is essential for efficient lariat intermediate export. These findings challenge previous notions about quality control mechanisms in mRNA export and shed light on novel steps in the export process.

Stats

By smRNA FISH in budding yeast, direct observation of nuclear export of lariat intermediates.
Export of lariat intermediates requires Mex67p and its adaptors Nab2p, Yra1p, and Nlp3.
Deletion of MLP1 reduces β-galactosidase activity by 50% for brG-IRES reporter.
The yra1-KR-all mutation reduces β-galactosidase activity by 52% for brG-IRES reporter.
The tom1Δ mutation significantly reduces β-galactosidase activity for brG-IRES reporter.

Quotes

"The data indicate that the nuclear basket can promote immature mRNP export."
"Our results challenge a general role for Mlp1p in quality control mechanisms."

Key Insights Distilled From

Export of discarded splicing intermediates requires mRNA export factors and the nuclear basket

by Zeng,Y., Sta... at www.biorxiv.org 10-14-2022

https://www.biorxiv.org/content/10.1101/2022.10.13.511998v2

Deeper Inquiries

How does the interaction between Nab2p and Mlp1p facilitate lariat intermediate export?

The interaction between Nab2p and Mlp1p plays a crucial role in facilitating lariat intermediate export. Nab2p, an mRNA export adapter, interacts directly with Mlp1p, a component of the nuclear basket at the NPC. This interaction is essential for recruiting lariat intermediates to the NPC for export to the cytoplasm. By binding to Nab2p, which is already associated with Mex67p-Mtr2p (the general mRNA export receptor), Mlp1p helps tether lariat intermediates to the nuclear basket, positioning them for efficient transit through the nuclear pore complex.

How might these findings impact our understanding of RNA quality control mechanisms?

These findings challenge traditional views on RNA quality control mechanisms by revealing that factors like Mlp1p do not act as strict quality control factors but instead promote the export of immature RNAs such as discarded lariat intermediates. The data suggest that rather than retaining faulty RNAs in the nucleus, certain components like Mlp1 can actually facilitate their transport out of the nucleus. This implies a more dynamic and nuanced role for factors implicated in nuclear retention and decay processes.

What implications do these discoveries have for our understanding of mRNA processing pathways?

The discoveries regarding lariat intermediate export shed light on how mRNA processing pathways are interconnected with mRNA export mechanisms. The fact that both mRNAs and discarded splicing intermediates utilize common machinery for export highlights a shared pathway involved in transporting different types of RNA molecules from the nucleus to the cytoplasm. Understanding this crosstalk between splicing fidelity mechanisms and mRNA export pathways provides insights into how cells ensure proper gene expression by efficiently exporting mature mRNAs while also clearing out aberrant or incomplete transcripts through dedicated processes within the cell's regulatory network.