Macronuclear DNA of Tetrahymena thermophila exists as defined subchromosomal-sized molecules.

Using the method of orthogonal-field-alternation gel electrophoresis, we have resolved the macronuclear DNA of Tetrahymena thermophila into a series of distinct bands. Using electrode switching intervals ranging from 10 to 70 seconds we have resolved DNA bands ranging in size from about 21 kb up to and beyond the size of yeast chromosomes VII and XV. Hybridization of Southern blots from these gels to both unique and repetitive DNA sequences shows that the macronuclear genome of T. thermophila has a precise organization. The unique sequences tested each hybridize to only one band of macronuclear DNA and the hybridization patterns seem to be identical in several inbred strains examined.