Related Experiment Videos
The 5'-end structure of ovalbumin mRNA in isolated nuclei and polysomes
R A Kopper1, T Stallcup, G Hufford
1Department of Chemistry, Hendrix College, Conway, AR 72032.
Abstract:
We used the chemical reagents dimethylsulfate and 4'-aminomethyl-4,5',8-trimethylpsoralen and the enzyme T1 ribonuclease to compare the 5'-end structure of ovalbumin mRNA in situ in purified hen oviduct nuclei and polysomes with that of the isolated mRNA. The qualitative pattern of structure-dependent base modifications and T1 ribonuclease cleavage sites in intranuclear and polysomal ovalbumin mRNAs was found to be nearly identical to those in isolated ovalbumin mRNA. These structural data are consistent with the presence of a trigonal stem-loop structure at the 5'-end of ovalbumin mRNA (hairpin-1) in nuclei and polysomes. Similar results were obtained for a coding region structure (hairpin-3) in intranuclear ovalbumin mRNA. We have recently shown that hairpin-1 positively affects the rate of ovalbumin mRNA translation in vitro and is part of a high affinity binding site for eucaryotic initiation factor-2 (eIF-2). The presence of hairpin-1 in ovalbumin mRNA in both a pretranslation state (nuclei) and active translation state (polysomes) is consistent with its hypothesized biological function as an intracellular initiation signal that facilitates the translation of this mRNA.
Insights
Ovalbumin mRNA maintains a specific 5'-end structure, hairpin-1, in both nuclei and polysomes. This structure is crucial for initiating ovalbumin mRNA translation by binding to eukaryotic initiation factor-2 (eIF-2).
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Ovalbumin mRNA translation is regulated by specific structural elements.
- The 5'-end of mRNA plays a critical role in translation initiation.
- Eukaryotic initiation factor-2 (eIF-2) is essential for initiating protein synthesis.
Purpose of the Study:
- To investigate the in situ 5'-end structure of ovalbumin mRNA in hen oviduct nuclei and polysomes.
- To compare the structure of intranuclear and polysomal ovalbumin mRNA with isolated mRNA.
- To confirm the role of the 5'-end hairpin-1 structure in translation initiation.
Main Methods:
- Chemical modification using dimethylsulfate and 4'-aminomethyl-4,5',8-trimethylpsoralen.
- Enzymatic cleavage using T1 ribonuclease.
- Analysis of RNA structure in purified hen oviduct nuclei, polysomes, and isolated mRNA.
Main Results:
- The 5'-end structure of ovalbumin mRNA in nuclei and polysomes is nearly identical to isolated mRNA.
- A trigonal stem-loop structure (hairpin-1) at the 5'-end of ovalbumin mRNA is present in both pre-translation and translation states.
- A coding region structure (hairpin-3) was also identified in intranuclear ovalbumin mRNA.
Conclusions:
- The 5'-end hairpin-1 structure of ovalbumin mRNA is conserved in vivo and facilitates translation initiation.
- Hairpin-1 acts as an intracellular initiation signal by binding to eukaryotic initiation factor-2 (eIF-2).
- These findings support the biological function of hairpin-1 in regulating ovalbumin mRNA translation.