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DNA synthesis associated with a DNA-nuclear-membrane complex from rat liver
Abstract:
Ultrastructural analysis of M-band from nuclei of rat liver showed small amounts of chromatin, fragments of inner nuclear membrane, some amorphous nuclear material, and nucleopores. The outer nuclear membrane with its associated ribosomes was removed by Sarkosyl during the preparation of M-band sample. Morphological features of nucleopores and the inner nuclear membrane were confirmed by freez-fracture technique. The gross chemical composition of the M-band was similar to that of nuclear-membrane fractions prepared by other techniques. The M-band contained the greatest proportion of newly-labeled DNA and also supported DNA synthesis in vitro. Electron-microscopic autoradiography of the M-band showed localization of silver grains of thymidine-3H presumably over newly synthesized DNA. The DNA synthesis could not be attributed to spurious attachment of DNA polymerase to M-band during its isolation. It was partially removed from the M-band by treatment with 0.5 M KC1, phospholipase A or C; and completely, by the action of pancreatic DNase. DNA synthesis was greater in M-band fractions isolated from nuclei of 24-hour regenerating liver.
Insights
The M-band, a nuclear structure, contains newly synthesized DNA and supports DNA replication. This process is enhanced in regenerating liver cells, indicating the M-band
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The nuclear envelope, composed of inner and outer membranes, plays a crucial role in cellular processes.
- The M-band, a component of the nuclear envelope, has been investigated for its role in DNA metabolism.
Purpose of the Study:
- To investigate the ultrastructural composition and biochemical properties of the M-band.
- To determine the M-band's role in DNA synthesis and its localization within the nucleus.
Main Methods:
- Ultrastructural analysis using electron microscopy.
- Freeze-fracture technique to examine membrane structures.
- Electron microscopic autoradiography with thymidine-3H to track DNA synthesis.
- Biochemical assays to determine M-band composition and associated enzymes.
Main Results:
- The M-band consists of chromatin, inner nuclear membrane fragments, and nucleopores.
- The M-band contains the majority of newly labeled DNA and supports in vitro DNA synthesis.
- DNA synthesis activity is significantly higher in M-band fractions from regenerating liver nuclei.
Conclusions:
- The M-band is a site of active DNA synthesis within the nucleus.
- Its composition and function are linked to DNA replication and repair processes.
- The M-band's role in DNA synthesis is particularly pronounced during liver regeneration.