Abstract
Several clones of reconstituted cells were isolated by fusion of karyoplasts of mouse melanoma B16 cells with cytoplasts of rat myoblastic L6 cells and processed by the mica-press-adsorption method for electron microscopy. Extrachromosomal small circular DNAs of less than 1 micron in contour length (smaller circular DNA) were present in both parental cells, and circles larger than 1 micron (larger circular DNA) were found more frequently in reconstituted cells at an early stage after the clonal isolation. Mitochondrial DNA was not released from mitochondria by this method. The new phenotypes of reconstituted cells were stable, but larger circles were lost after prolonged cultivation of the cells. The possibility that the larger circular DNAs result from intrachromosomal DNA rearrangement induced by rat cytoplasts is discussed.
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