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Fidelity of histone synthesis in cultured human fibroblasts
Abstract:
The results in the literature to support Orgel's general error hypothesis of ageing only provide indirect evidence that errors in protein synthesis increase during senescence. This study attempts to provide direct evidence of errors in protein synthesis by measuring the misincorporation of 35S-methionine into histone H1 obtained from young and old fibroblasts (MRC-5). The conclusions that can be drawn from this study are: (a) the error level for the misincorporation of methionine into histone H1 is less than 7 methionines/10(5) amino acids and 2-3 methionines/10(4) amino acids in young and old cells respectively; (b) a methionine containing fraction associated with H1 is obtained after the final purification. The amount of this fraction increases with the age of the cell culture as does the number of methionine residues; (c) there is a variation in the complexity of H1 polypeptide chains, the complexity increasing with the age of cultured cells.
Insights
Errors in protein synthesis increase with age, directly evidenced by methionine misincorporation into histone H1 in aging fibroblasts. This study quantifies these errors, revealing age-related increases in misincorporated methionine and H1 polypeptide complexity.
Area of Science:
- Biogerontology
- Molecular Biology
- Cellular Aging
Background:
- Orgel's error hypothesis suggests increased protein synthesis errors contribute to aging.
- Existing literature provides only indirect evidence for this hypothesis.
- Direct measurement of protein synthesis errors in aging cells is needed.
Purpose of the Study:
- To provide direct evidence for increased protein synthesis errors during senescence.
- To quantify methionine misincorporation into histone H1 in young versus old fibroblasts.
- To investigate age-related changes in histone H1 polypeptide complexity.
Main Methods:
- Utilized young and old MRC-5 fibroblasts.
- Measured the misincorporation of 35S-methionine into purified histone H1.
- Analyzed methionine-containing fractions associated with H1.
- Assessed the complexity of H1 polypeptide chains.
Main Results:
- Methionine misincorporation into histone H1 was low (<7/10^5 amino acids in young, 2-3/10^4 in old cells).
- A methionine-containing fraction associated with H1 increased with cell culture age.
- Histone H1 polypeptide chain complexity increased with cell culture age.
Conclusions:
- Direct evidence supports increased protein synthesis errors in aging cells.
- Age-related accumulation of misincorporated methionine in histone H1 was observed.
- Increased complexity of histone H1 suggests age-associated alterations in protein structure and synthesis.