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Intracellular location of small circular DNA complexes in mammalian cell lines
Abstract:
For determination of the cellular location of small polydisperse circular DNA complexes, rat myoblastic L6 cells, HeLa cells, and mouse L cells were enucleated and processed by the micapress-adsorption method for electron microscopy (H. Yamagishi, T. Kunisada, and T. Tsuda, 1982, Plasmid 8, 299-306). Small circular DNA complexes from intact cells showed a heterogeneous size distribution of from 0.1 to more than 2 micron with a mean contour length of 0.6 to 0.8 micron, like that of covalently closed circular DNAs. Cells contained 400 to 1200 copies. The size distribution in the cytoplasts was narrow and the number-average length was 0.3 to 0.4 micron, whereas that in L6 karyoplasts was wide and the average length was 0.9 micron. The longer circular complexes appeared to be absent from the cytoplasts. The origin and biological functions of these complexes are discussed in relation to the cellular locations of the complexes.
Insights
Researchers investigated the cellular location of small polydisperse circular DNA complexes using electron microscopy. Findings indicate these DNA complexes are primarily located in the nucleus, with distinct size distributions in different cellular components.
Area of Science:
- Cell Biology
- Molecular Genetics
- Biophysics
Background:
- Small polydisperse circular DNA complexes are found in various cell types.
- Their cellular localization and biological significance remain incompletely understood.
Purpose of the Study:
- To determine the precise cellular location of small polydisperse circular DNA complexes.
- To analyze the size distribution and copy number of these DNA complexes within different cellular compartments.
Main Methods:
- Micapress-adsorption method for electron microscopy was employed.
- Enucleation of rat myoblastic L6 cells, HeLa cells, and mouse L cells.
- Analysis of DNA complex size distribution in intact cells, cytoplasts, and karyoplasts.
Main Results:
- Intact cells contained 400-1200 copies of circular DNA complexes with heterogeneous sizes (0.1 to >2 micron).
- Cytoplasts showed a narrow size distribution (0.3-0.4 micron), while L6 karyoplasts had a wider distribution (0.9 micron).
- Larger circular DNA complexes were notably absent from cytoplasts.
Conclusions:
- Cellular location of small polydisperse circular DNA complexes is predominantly nuclear.
- Size distribution varies significantly between nuclear and cytoplasmic fractions.
- Further research is needed to elucidate the origin and biological functions of these complexes based on their cellular distribution.