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A turnover pathway for both stable and unstable mRNAs in yeast: evidence for a requirement for deadenylation
1Department of Molecular and Cellular Biology, University of Arizona, Tucson 85721.
Abstract:
To determine pathways of mRNA turnover in yeast, we have followed the poly(A) tail removal and degradation of a pulse of newly synthesized transcripts from four different genes. Before decay of both stable and unstable mRNAs initiated, there was a temporal lag during which the poly(A) tail was deadenylated to an oligo(A) length. Altering the deadenylation rate of an mRNA led to a corresponding change in the length of this lag. The rate of deadenylation and the stability of the oligo(A) species varied between mRNAs, explaining the differences in mRNA half-lives. To examine how the transcript body was degraded following deadenylation, we used the strategy of inserting strong RNA secondary structures, which can slow exonucleolytic digestion and thereby trap decay intermediates, into the 3' UTR of mRNAs. Fragments lacking the 5' portion of two different mRNAs accumulated after deadenylation as full-length mRNA levels decreased. Therefore, these results define an mRNA decay pathway in which deadenylation leads to either internal cleavage or decapping followed by 5'-->3' exonucleolytic degradation of the mRNA.
Insights
This study reveals that messenger RNA (mRNA) decay in yeast begins with poly(A) tail shortening, followed by transcript body degradation. This process explains variations in mRNA stability and turnover rates.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Messenger RNA (mRNA) turnover is crucial for gene expression regulation.
- Understanding mRNA decay pathways is essential for comprehending cellular processes.
Purpose of the Study:
- To elucidate the specific pathways of mRNA turnover in yeast.
- To investigate the roles of poly(A) tail removal and transcript body degradation.
Main Methods:
- Tracking poly(A) tail removal and degradation of newly synthesized transcripts from four yeast genes.
- Utilizing RNA secondary structures in the 3' untranslated region (UTR) to trap decay intermediates.
- Analyzing accumulation of mRNA fragments to infer degradation mechanisms.
Main Results:
- mRNA decay initiates with a lag phase of poly(A) tail deadenylation to an oligo(A) length.
- Deadenylation rate directly influences the lag phase duration and mRNA half-life.
- Transcript body degradation follows deadenylation, involving internal cleavage or decapping and 5' to 3' exonucleolytic digestion.
Conclusions:
- A conserved mRNA decay pathway in yeast involves deadenylation preceding transcript body degradation.
- Variations in deadenylation rates and oligo(A) stability contribute to differential mRNA half-lives.
- The findings define a sequential model of mRNA turnover: deadenylation, followed by cleavage or decapping/exonucleolytic degradation.