Cryo-EM Structures Reveal Mechanism for Initiating Spliceosome Disassembly After Pre-mRNA Splicing

Core Concepts

The disassembly of the multi-megadalton spliceosome complex is initiated by the coordinated action of disassembly factors and the RNA helicase DHX15, which target the catalytic U6 snRNA to trigger the disassembly process after pre-mRNA splicing is complete.

Abstract

The article presents cryo-electron microscopy (cryo-EM) structures of the terminal intron-lariat spliceosome from nematodes and humans, along with biochemical and genetic data, to elucidate the mechanism of spliceosome disassembly.
Key insights:

Spliceosome disassembly is initiated by four disassembly factors and the conserved RNA helicase DHX15.
The disassembly factors probe the large inner and outer surfaces of the spliceosome to detect the release of the ligated mRNA.
Two disassembly factors, TFIP11 and C19L1, along with three general spliceosome subunits (SYF1, SYF2, and SDE2), dock and activate the DHX15 helicase on the catalytic U6 small nuclear RNA (snRNA) to trigger the disassembly process.
The U6 snRNA controls both the start and end of pre-mRNA splicing, as it is involved in the initiation of spliceosome assembly and the initiation of spliceosome disassembly.
The findings provide a framework to understand the general control of spliceosomal RNA helicases and the discard of aberrant spliceosomes.

Stats

The cryo-EM structures were determined at resolutions ranging from 2.6 to 3.2 Angstroms.

Quotes

"Our results uncover how four disassembly factors and the conserved RNA helicase DHX15 initiate spliceosome disassembly."
"U6 thus controls both the start and end of pre-mRNA splicing."

Key Insights Distilled From

Mechanism for the initiation of spliceosome disassembly - Nature

by Matt... at www.nature.com 06-26-2024

https://www.nature.com/articles/s41586-024-07741-1

Deeper Inquiries

How do the disassembly factors and DHX15 helicase coordinate their activities to ensure the efficient and timely disassembly of the spliceosome?

The disassembly factors, including TFIP11, C19L1, SYF1, SYF2, and SDE2, play crucial roles in initiating spliceosome disassembly by probing the spliceosome surfaces to detect the release of ligated mRNA. Once the ligated mRNA is detected, TFIP11 and C19L1, along with SYF1, SYF2, and SDE2, facilitate the docking and activation of the RNA helicase DHX15 on the catalytic U6 snRNA. DHX15 then acts on the U6 snRNA to initiate the disassembly process. This coordination ensures that the spliceosome is efficiently and timely disassembled, allowing for the recycling of its components and the completion of the splicing cycle.

What are the potential implications of the spliceosome disassembly mechanism for the regulation of gene expression and the maintenance of cellular homeostasis?

The spliceosome disassembly mechanism has significant implications for the regulation of gene expression and the maintenance of cellular homeostasis. Efficient spliceosome disassembly is essential for the accurate and timely processing of pre-mRNA, which directly impacts gene expression. Dysregulation of spliceosome disassembly can lead to errors in splicing, resulting in aberrant mRNA transcripts and potentially disrupting cellular functions. By understanding the molecular basis of spliceosome disassembly, researchers can gain insights into how gene expression is regulated at the post-transcriptional level and how cells maintain the balance required for proper cellular function.

What other cellular processes or complexes might utilize a similar mechanism of helicase-mediated disassembly to control the dynamics and recycling of macromolecular complexes?

Several other cellular processes and complexes utilize a similar mechanism of helicase-mediated disassembly to control the dynamics and recycling of macromolecular complexes. For example, the exosome complex, involved in RNA degradation and processing, utilizes RNA helicases to unwind RNA substrates for degradation. Additionally, the replisome, responsible for DNA replication, employs helicases to unwind the DNA double helix during replication. Similarly, ribosomes, the cellular machinery for protein synthesis, require helicases for the recycling of ribosomal subunits after translation. These examples highlight the widespread use of helicase-mediated disassembly in various cellular processes to ensure the efficient turnover and recycling of macromolecular complexes.