Cloning of Escherichia coli genes encoding 3-methyladenine DNA glycosylases I and II

Summary The presence of polydisperse small circular DNAs in wheat cells was first confirmed by the mica-pressadsorption (MPA) method for electron microscopy. To identify their location in the cell, chloroplast and mitochondrial fractions were examined separately by the same method; small circular DNAs were scarcely found in the former but abundantly in the latter fraction, indicating their origin from mitochondria. The size varied greatly, ranging from 0.1 to 2.0 m in contour length. To verify the present finding, the same mitochondrial fraction was examined by the conventional cytochrome-spreading method by which the presence of the same size-class of circular DNAs was confirmed.To know the relationship between the small circular DNAs and cytoplasmic differentiation observed among Tritium (wheat) and Aegilops species, protoplasts isolated from seven alloplasmic lines of common wheat with different cytoplasms were examined by the MPA method. Similar polydisperse small circular DNAs, ranging from 0.1 to 2.5 m in contour length Dere found in all lines, and no clear size differences were noticed among the DNA populations from the cytoplasms of eight Triticum and Aegilops species.