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mRNA destabilization triggered by premature translational termination depends on at least three cis-acting sequence
S W Peltz1, A H Brown, A Jacobson
1Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655.
Abstract:
Nonsense mutations in a gene can accelerate the decay rate of the mRNA transcribed from that gene, a phenomenon we describe as nonsense-mediated mRNA decay. Using amber (UAG) mutants of the yeast PGK1 gene as a model system, we find that nonsense-mediated mRNA decay is position dependent, that is, nonsense mutations within the initial two-thirds of the PGK1-coding region accelerate the decay rate of the PGK1 transcript < or = 12-fold, whereas nonsense mutations within the carboxy-terminal third of the coding region have no effect on mRNA decay. Moreover, we find that this position effect reflects (1) a requirement for sequences 3' to the nonsense mutation that may be necessary for translational reinitiation or pausing, and (2) the presence of an additional sequence that, when translated, inactivates the nonsense-mediated mRNA decay pathway. This stabilizing element is positioned within the coding region such that it constitutes the boundary between nonsense mutations that do or do not affect mRNA decay. Rapid decay of PGK1 nonsense-containing transcripts is also dependent on the status of the UPF1 gene. Regardless of the position of an amber codon in the PGK1 gene, deletion of the UPF1 gene restores wild-type decay rates to nonsense-containing PGK1 transcripts.
Insights
Nonsense mutations trigger faster mRNA decay, but only in the first two-thirds of the yeast PGK1 gene. A specific sequence and the UPF1 gene influence this nonsense-mediated mRNA decay pathway.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Nonsense mutations can trigger mRNA decay, impacting gene expression.
- The mechanisms and positional effects of nonsense-mediated mRNA decay are not fully understood.
Purpose of the Study:
- To investigate the positional dependence of nonsense-mediated mRNA decay.
- To identify factors influencing mRNA decay rates in response to nonsense mutations.
Main Methods:
- Utilized amber (UAG) mutants of the yeast PGK1 gene as a model system.
- Analyzed mRNA decay rates based on nonsense mutation location.
- Assessed the role of the UPF1 gene in the decay pathway.
Main Results:
- Nonsense mutations in the initial two-thirds of the PGK1 gene accelerated mRNA decay up to 12-fold.
- Mutations in the carboxy-terminal third had no effect on mRNA decay.
- A stabilizing element and the UPF1 gene were identified as key regulators of this decay process.
Conclusions:
- Nonsense-mediated mRNA decay is position-dependent in the PGK1 gene.
- Translational reinitiation/pausing sequences and a specific stabilizing element dictate decay rates.
- UPF1 gene status is critical for rapid decay of nonsense-containing transcripts.