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Studies on Acetabularia chloroplast DNA Muir, Bernice L.


The physical properties and renaturation kinetics of DNA extracted from isolated chloroplasts of Acetabulavia meditewanea has been studied. 3 It has a buoyant density of 1.702 g/cm³ , which corresponds to a base composition of 42.8% G+C. When melted in SSC, Acetabulavia chloroplast DNA has a Tm of 86.7°, corresponding to a base composition of 43% G+C. The close agreement of the base compositions calculated from the buoyant density and the melting temperature indicates the absence of unusual bases in Acetdbularia meditewanea chloroplast DNA. In 0.1 x SSC, Acetabulavia chloroplast DNA melts with a Tm of 70.7°, and the melting transition is very broad. The breadth of the melting transition suggests that this DNA has a high degree of intramolecular heterogeneity. A differential plot of the thermal transition of A. meditewanea chloroplast DNA supports this conclusion. The buoyant densities of DNA from bacterial contaminants found in Acetabulavia cultures differed from the buoyant density of the chloroplast DNA. In any case, the amount of bacterial contamination was too low to account for any of the results obtained. Renaturation experiments indicate a kinetic complexity of 1.1 x 10⁹ daltons from Acetabulavia meditewanea chloroplast DNA. As a result of uncertainties in the values of alkaline sedimentation coefficients, this calculated kinetic complexity may be too low. The possible genetic information contained in the chloroplast DNA of Acetabulavia meditewanea is discussed.

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