Abstract
When Acetabularia cliftonii chloroplast DNA ( ϱ = 1.706 g/cm 3) is centrifuged in an ethidium bromide-CsCl gradient, the lower band is enriched for DNA with a buoyant density of 1.712 g/cm 3 containing small covalently closed circular molecules. The minicircles measure 4.15 ± 0.30 μm in the closed conformation and 4.35 ± 0.20 μm in the open conformation. They are not of nuclear or bacterial origin, and appear to exist as independent entities within the chloroplast, although a mitochondrial origin cannot be completely ruled out. No 40–45 μm circles, as found in other chloroplasts, were found in either ethidium bromide-CsCl fraction. None were found in total chloroplast DNA by any of a number of methods tried. Linear molecules up to 200 μm were measured in chloroplast lysates. The main chloroplast genome may consist of very large circular molecules which are broken by even small shear forces.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Nucleic Acids and Protein Synthesis
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