Green B R
Biochim Biophys Acta. 1976 Oct 4;447(2):156-66. doi: 10.1016/0005-2787(76)90339-7.
When Acetabularia cliftonii chloroplast DNA (p = 1.706 g/cm3) is centrifuged in an ethidium bromide-CsCl gradient, the lower band is enriched for DNA with a buoyant density of 1.712 g/cm3 containing small covalently closed circular molecules. The minicircles measure 4.15 +/- 0.30 mum in the closed conformation and 4.35 +/- 0.20 mum 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 mum 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 mum were measured in chloroplast lysates. The main chloroplast genome may consist of very large circular molecules which are broken by even small shear forces.
当将克利夫顿伞藻叶绿体DNA（p = 1.706 g/cm³）在溴化乙锭 - 氯化铯梯度中离心时，较低的条带富含浮力密度为1.712 g/cm³的DNA，其中包含小的共价闭合环状分子。这些微小环在闭合构象下的尺寸为4.15±0.30μm，在开放构象下为4.35±0.20μm。它们并非源自细胞核或细菌，尽管不能完全排除线粒体起源，但似乎作为叶绿体中的独立实体存在。在溴化乙锭 - 氯化铯组分中均未发现其他叶绿体中存在的40 - 45μm的环。通过多种尝试的方法在总叶绿体DNA中均未发现此类环。在叶绿体裂解物中测量到了长达200μm的线性分子。主要的叶绿体基因组可能由非常大的环状分子组成，这些分子甚至会被很小的剪切力破坏。
