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Ribosomal DNA in spores of Physarum polycephalum
Abstract:
DNA was isolated from plasmodia, spores and newly hatched amoebae of the slime mould Physarum polycephalum. The DNA preparations were fractionated in CsCl gradients and each fraction hybridised to combined 19 S + 26 S rRNA. In all three DNA preparations hybridisation was found to be limited to satellite DNA (rho = 1.714 g/cm3) and at saturation was found to reach a level of 0.16--0.18 % of total DNA. The main band of nuclear DNA (rho = 1.702 g/cm3) did not hybridise appreciably. Further experiments using analytical CsCl gradients revealed that the ratio of satellite to main band DNA was similar in all three preparations. It is concluded that the genes for ribosomal RNA are equally reiterated in spores, hatching amoebae and in plasmodia. They appear to be similarly organised in all stages of the life cycle examined so far.
Insights
Ribosomal RNA genes in the slime mould Physarum polycephalum are located in satellite DNA. Their organization and reiteration are consistent across plasmodia, spores, and amoebae stages.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- The slime mould Physarum polycephalum exhibits distinct life cycle stages, including plasmodia, spores, and amoebae.
- Understanding the organization and reiteration of ribosomal RNA (rRNA) genes is crucial for comprehending gene regulation and genome evolution.
Purpose of the Study:
- To investigate the location and abundance of ribosomal RNA genes in different life cycle stages of Physarum polycephalum.
- To determine if the organization of rRNA genes varies between plasmodial, spore, and amoebal forms.
Main Methods:
- DNA isolation from plasmodia, spores, and newly hatched amoebae.
- Fractionation of DNA using Cesium Chloride (CsCl) density gradients.
- Hybridization of DNA fractions with 19 S + 26 S ribosomal RNA (rRNA).
Main Results:
- Ribosomal RNA gene hybridization was exclusively observed in satellite DNA (density = 1.714 g/cm3) across all tested life stages.
- Satellite DNA constituted 0.16-0.18% of total DNA at saturation.
- The main band nuclear DNA (density = 1.702 g/cm3) showed negligible hybridization.
- The ratio of satellite DNA to main band DNA remained consistent among plasmodia, spores, and amoebae.
Conclusions:
- The genes for ribosomal RNA in Physarum polycephalum are located within satellite DNA.
- The reiteration level and organization of rRNA genes are similar in plasmodia, spores, and amoebae.
- rRNA gene organization appears conserved throughout the examined life cycle stages of Physarum polycephalum.