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Interruptions in single strands of the DNA in slime mold and other organisms
Abstract:
The molecular weight of single-stranded DNA from the slime mold Physarum polycephalum has been determined by alkaline gradient centrifugation. The average molecular weight during DNA synthesis ( approximately 1.5 x 10(7) D) is less than that observed in nonsynthetic periods ( approximately 4 x 10(7) D). On the basis of a chromosome number of 50 per nucleus and a DNA content of 1 mumug per nucleus, we are led to conclude that at pH 12 each chromosome dissociates into 300 (single-stranded) pieces of DNA. We have also compared the sedimentation profiles of single-stranded DNA from Escherichia coli, PPLO, and T2 bacteriophage. These data support the conjecture that each bacterial chromosome can be dissociated into 10 or 12 single-stranded pieces of DNA. Dissociation of DNA into multiple pieces under our experimental conditions is best interpreted in terms of interruptions in the continuity of the DNA either by naturally occurring gaps or at alkali-labile bonds.
Insights
Single-stranded DNA molecular weight in Physarum polycephalum varies with DNA synthesis. Each chromosome breaks into many single-stranded DNA pieces, suggesting natural DNA gaps or alkali-labile bonds.
Area of Science:
- Molecular Biology
- Biochemistry
Background:
- Understanding DNA structure and integrity is crucial in molecular biology.
- The slime mold Physarum polycephalum offers a model for studying DNA dynamics.
Purpose of the Study:
- To determine the molecular weight of single-stranded DNA in Physarum polycephalum.
- To investigate DNA fragmentation during different cellular processes.
- To compare DNA dissociation patterns across different organisms.
Main Methods:
- Alkaline gradient centrifugation was used to determine DNA molecular weight.
- Sedimentation profiles of single-stranded DNA from various sources were analyzed.
Main Results:
- The average molecular weight of single-stranded DNA during synthesis (1.5 x 10^7 D) is lower than during nonsynthetic periods (4 x 10^7 D).
- Each Physarum polycephalum chromosome appears to dissociate into approximately 300 single-stranded DNA pieces.
- Bacterial chromosomes (E. coli, PPLO, T2 bacteriophage) showed dissociation into 10-12 single-stranded DNA pieces.
Conclusions:
- DNA dissociation into multiple pieces suggests inherent interruptions, such as natural gaps or alkali-labile bonds.
- These findings provide insights into the structural organization of DNA within chromosomes.
- Comparative analysis highlights potential differences in DNA integrity across species.