mRNA 3' tagging is induced by nonsense-mediated decay and promotes ribosome dissociation
Igor Y Morozov1, Meriel G Jones, Peter D Gould
1The University of Liverpool, Institute of Integrative Biology, Liverpool, United Kingdom.
Abstract:
For a range of eukaryote transcripts, the initiation of degradation is coincident with the addition of a short pyrimidine tag at the 3' end. Previously, cytoplasmic mRNA tagging has been observed for human and fungal transcripts. We now report that Arabidopsis thaliana mRNA is subject to 3' tagging with U and C nucleotides, as in Aspergillus nidulans. Mutations that disrupt tagging, including A. nidulans cutA and a newly characterized gene, cutB, retard transcript degradation. Importantly, nonsense-mediated decay (NMD), a major checkpoint for transcript fidelity, elicits 3' tagging of transcripts containing a premature termination codon (PTC). Although PTC-induced transcript degradation does not require 3' tagging, subsequent dissociation of mRNA from ribosomes is retarded in tagging mutants. Additionally, tagging of wild-type and NMD-inducing transcripts is greatly reduced in strains lacking Upf1, a conserved NMD factor also required for human histone mRNA tagging. We argue that PTC-induced translational termination differs fundamentally from normal termination in polyadenylated transcripts, as it leads to transcript degradation and prevents rather than facilitates further translation. Furthermore, transcript deadenylation and the consequent dissociation of poly(A) binding protein will result in PTC-like termination events which recruit Upf1, resulting in mRNA 3' tagging, ribosome clearance, and transcript degradation.
Insights
Arabidopsis thaliana mRNA undergoes 3' end tagging with pyrimidines, similar to fungi. This tagging, involving nonsense-mediated decay (NMD) and the Upf1 factor, regulates transcript degradation.
Area of Science:
- Molecular Biology
- Genetics
- Plant Science
Background:
- Eukaryotic transcript degradation often involves 3' end pyrimidine tagging.
- Cytoplasmic mRNA tagging is known in human and fungal systems.
- Arabidopsis thaliana is a model organism for plant molecular biology.
Purpose of the Study:
- To investigate 3' end mRNA tagging in Arabidopsis thaliana.
- To determine the role of tagging in transcript degradation and nonsense-mediated decay (NMD).
- To identify genes involved in the tagging process.
Main Methods:
- Analysis of mRNA tagging in wild-type and mutant Arabidopsis thaliana strains.
- Investigating the role of nonsense-mediated decay (NMD) in tagging.
- Characterizing the function of newly identified genes (cutB) and known genes (cutA, Upf1) in the process.
Main Results:
- Arabidopsis thaliana mRNA is tagged with U and C nucleotides at the 3' end.
- Mutations in tagging genes (cutA, cutB) slow down transcript degradation.
- Nonsense-mediated decay (NMD) elicits 3' tagging of transcripts with premature termination codons (PTCs).
- Tagging mutants show retarded dissociation of mRNA from ribosomes after PTCs.
- Tagging is significantly reduced in strains lacking Upf1, a key NMD factor.
Conclusions:
- 3' end pyrimidine tagging is a conserved mechanism in eukaryotes, including plants.
- Tagging plays a role in regulating transcript degradation, particularly in response to PTCs via NMD.
- PTC-induced termination differs from normal termination, leading to degradation and involving Upf1-mediated tagging and ribosome clearance.
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