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An additional editing site is present in apolipoprotein B mRNA
N Navaratnam1, D Patel, R R Shah
1MRC Clinical Research Centre, Harrow, Middlesex, UK.
Nucleic Acids Research
|April 25, 1991
Summary
Human intestinal apolipoprotein B mRNA editing occurs at a second site, nucleotide 6802, in addition to the known site at nucleotide 6666. This discovery reveals a new mechanism in apo B48 protein formation.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Apolipoprotein B (apo B) mRNA undergoes RNA editing in the human intestine.
- This editing at nucleotide 6666 creates a stop codon, defining apo B48.
Purpose of the Study:
- To investigate additional RNA editing sites in human intestinal apo B mRNA.
- To identify sequences critical for RNA editing recognition.
Main Methods:
- Analysis of human intestinal cDNAs spanning nucleotide 6666.
- In vitro editing assays using synthetic RNA and intestinal extracts.
- Sequence analysis to identify editing recognition sites.
Main Results:
- Two of eleven cDNAs showed editing at both nucleotide 6666 and a novel site, nucleotide 6802.
- Editing at nucleotide 6802 converts a threonine codon to isoleucine.
- In vitro editing efficiency at nucleotide 6802 was 10-15% of that at nucleotide 6666.
- A specific sequence was identified as important for editing recognition.
- No other editing sites were found in the analyzed region, and no structural homology was observed between the two sites.
Conclusions:
- Human intestinal apo B mRNA exhibits editing at a second site (nucleotide 6802) besides the known site (nucleotide 6666).
- This additional editing site contributes to the diversity of apo B protein isoforms.
- The editing process is sequence-specific and does not rely on secondary structural homology between sites.