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Multiple splice forms of ribonuclease-inhibitor mRNA differ in the 5'-untranslated region
D Crawford1, K Hagerty, B Beutler
1Howard Hughes Medical Institute, U.T. Southwestern Medical Center, Dallas 75235-9050.
Abstract:
We report the sequence of the cDNAs representing five independent splice forms of human placental RNase inhibitor (RI) mRNA. RI mRNAs differ principally in the 5'-untranslated region, which may include or lack a 68-nucleotide (nt) exon inserted at a splice site located only 20 nt upstream from the initiator AUG. At least three other exons may also abut the same splice site. This unusual and variable feature of the mRNA would suggest that secondary structure in the region of the start codon may differ among RI messages. A single copy of the RI gene exists in the human genome.
Insights
Researchers identified five splice variants of human placental ribonuclease inhibitor (RI) mRNA, primarily differing in their 5' untranslated regions. This structural variation may impact the secondary structure near the start codon, influencing gene expression.
Area of Science:
- Molecular Biology
- Genetics
- Gene Expression
Background:
- Ribonuclease inhibitor (RI) is crucial for protecting RNA from degradation.
- Understanding mRNA structure is key to regulating protein synthesis.
- Alternative splicing generates diverse mRNA transcripts from a single gene.
Purpose of the Study:
- To sequence and characterize the complementary DNAs (cDNAs) of human placental RNase inhibitor (RI) mRNA splice forms.
- To investigate the structural variations in the 5'-untranslated region (5'-UTR) of RI mRNA.
- To explore the potential implications of these variations on mRNA secondary structure and translation initiation.
Main Methods:
- Complementary DNA (cDNA) sequencing of five independent human placental RI mRNA splice forms.
- Analysis of splice junctions and nucleotide sequences, particularly in the 5'-UTR.
- Bioinformatic analysis to predict secondary structure in the 5'-UTR.
Main Results:
- Five distinct splice forms of human placental RI mRNA were identified.
- The primary difference among these splice forms lies in their 5'-UTRs, with variations in exon inclusion/exclusion.
- A specific 68-nucleotide exon can be alternatively spliced into the 5'-UTR, located near the initiator AUG codon.
- The human genome contains a single copy of the RI gene.
Conclusions:
- Alternative splicing of human placental RI mRNA leads to significant structural diversity in the 5'-UTR.
- These 5'-UTR variations, including the variable 68-nt exon, may influence mRNA secondary structure around the translation start site.
- Such structural differences could modulate RNase inhibitor (RI) protein expression levels.