Periodic organisation of foldback sequences in Physarum polycephalum nuclear DNA
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Abstract:
Nuclear DNA from the slime mould Physarum polycephalum is shown to contain interspersed inverted repeat sequences, such that denatured fragments of DNA containing pairs of these sequences form intra-chain duplexes under appropriate conditions. The organisation and distribution of the nucleotide sequences responsible for the formation of foldback structures in Physarum DNA have been investigated using the electron microscope. The majority of foldback duplexes have sizes ranging up to 800 base pairs, and about 60-80% of DNA molecules 2.2 X 10(4) bases in length contain interspersed foldback elements. The size of individual foldback duplexes, and also the length of the intervening sequences which separate them, are non-random. The results can best be explained by a model in which separate foldback foci in Physarum DNA are spaced periodically at regular intervals. The regions containing foldback foci are thought to contain smaller, tandemly-arranged sequences of discrete sizes, in some cases related to other nucleotide sequences of a similar nature in the same locality in Physarum DNA.
Insights
Nuclear DNA in Physarum polycephalum contains interspersed inverted repeats. These sequences form foldback structures, suggesting a periodic organization within the slime mold
Area of Science:
- Molecular Biology
- Genetics
- Eukaryotic Microbiology
Background:
- Nuclear DNA organization is crucial for genome stability and function.
- Inverted repeat sequences are known to form secondary structures in DNA.
- The slime mold Physarum polycephalum offers a unique model for studying eukaryotic DNA.
Purpose of the Study:
- To investigate the organization and distribution of foldback structures in Physarum polycephalum DNA.
- To characterize the nucleotide sequences responsible for foldback formation.
- To elucidate the spatial arrangement of these sequences within the genome.
Main Methods:
- Electron microscopy was employed to visualize DNA structures.
- Analysis of denatured DNA fragments under specific conditions to promote intra-chain duplex formation.
- Quantification of foldback duplex sizes and their distribution along DNA molecules.
Main Results:
- Physarum polycephalum DNA contains interspersed inverted repeat sequences.
- These sequences form intra-chain duplexes (foldback structures) up to 800 base pairs.
- Approximately 60-80% of DNA molecules exhibit these foldback elements.
- The spacing of foldback structures and intervening sequences is non-random, suggesting periodic organization.
- Foldback regions may contain tandemly arranged smaller sequences.
Conclusions:
- Physarum polycephalum DNA possesses a non-random, potentially periodic organization of foldback structures.
- This organization is mediated by interspersed inverted repeat sequences.
- The findings suggest a model of discrete, periodically spaced foldback foci within the genome.
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