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Nonsense mutations in the dihydrofolate reductase gene affect RNA processing
G Urlaub1, P J Mitchell, C J Ciudad
1Department of Biological Sciences, Columbia University, New York, New York 10027.
Molecular and Cellular Biology
|July 1, 1989
Summary
Nonsense mutations in the dihydrofolate reductase (dhfr) gene disrupt RNA processing, leading to reduced dhfr mRNA levels. This suggests a link between RNA splicing, nuclear transport, and translation in mammalian cells.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Dihydrofolate reductase (dhfr) is essential for DNA synthesis.
- Mutations in the dhfr gene can lead to cellular deficiencies.
- Understanding dhfr gene regulation is crucial for cell biology research.
Purpose of the Study:
- To investigate the impact of nonsense mutations on dhfr mRNA levels.
- To elucidate the mechanisms underlying dhfr gene expression regulation.
- To explore the relationship between RNA processing and translation.
Main Methods:
- Isolation and characterization of UV-induced DHFR-deficient mutants in Chinese hamster ovary cells.
- RNA heteroduplex mapping, gene cloning, enzymatic amplification, and DNA sequencing to identify mutations.
- Analysis of steady-state mRNA levels, nuclear run-on assays, and minigene transfections.
Main Results:
- Thirteen DHFR-deficient mutants were identified, with 11 point mutations and 2 large deletions.
- Ten of the 11 point mutations resulted in nonsense codons, causing a low-RNA phenotype.
- Transcription and mRNA stability were unaffected, indicating RNA processing is impaired.
Conclusions:
- Nonsense mutations in internal dhfr exons disrupt RNA processing, reducing mRNA levels.
- A model is proposed where splicing and nuclear transport are coupled to translation.
- The low-RNA phenotype was not observed in transfected genes, suggesting differential processing.