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Ultrastructure and template accessibility of modified chromatin in isolated macronuclei of Paramecium aurelia
Abstract:
Macronuclei of Paramecium aurelia, isolated in 4% gum arabic, contain nearly exclusively heterochromatin which is unaccessible to DNA-dependent, bacterial RNA polymerase. Heterochromatin decondensation under tris-HCl treatment did not change its template accessibility, whereas selective removal of the basic proteins induced profound changes in ultrastructure of heterochromatin and increased its template activity. More intensive incorporation of H3-UMP was found after arginine rich histones removal. The relations between functional and morphological changes after various heterochromatin modification in macronuclei of Paramecium aurelia, a representative of lower eukariotes, are discussed and compared with those in higher eukariotes.
Insights
Removing basic proteins from Paramecium aurelia macronuclei heterochromatin significantly altered its structure and increased template activity for RNA synthesis. This highlights the role of proteins in heterochromatin accessibility and function.
Area of Science:
- Cell Biology
- Molecular Biology
- Eukaryotic Gene Regulation
Background:
- Macronuclei in Paramecium aurelia are primarily composed of heterochromatin.
- Heterochromatin is generally considered transcriptionally inactive and inaccessible to polymerases.
Purpose of the Study:
- To investigate the relationship between heterochromatin structure and function in Paramecium aurelia.
- To determine the effect of protein removal on heterochromatin accessibility and template activity.
Main Methods:
- Isolation of Paramecium aurelia macronuclei.
- Treatment with tris-HCl for heterochromatin decondensation.
- Selective removal of basic proteins and histones.
- Assessing template accessibility using DNA-dependent bacterial RNA polymerase.
- Monitoring H3-UMP incorporation as a measure of RNA synthesis.
Main Results:
- Isolated macronuclei predominantly contained inaccessible heterochromatin.
- Tris-HCl treatment did not enhance template accessibility.
- Selective removal of basic proteins led to significant ultrastructural changes and increased template activity.
- Removal of arginine-rich histones resulted in more intensive H3-UMP incorporation.
Conclusions:
- Basic proteins, particularly arginine-rich histones, play a crucial role in maintaining heterochromatin structure and limiting its template activity in Paramecium aurelia.
- Functional and morphological changes in heterochromatin are closely linked.
- Findings in this lower eukaryote offer insights comparable to higher eukaryotes regarding heterochromatin regulation.