Frances M. Davis

Localization of highly repeated HindIII fragments of novikoff rat DNA to the nucleolus

Novlkoff rat ascltes hepatoma cells have large nucleoh compared to normal rat cells and nucleoli from these hepatoma cells have been isolated m high yield and purity [ 1 ] The nucleolus IS known to be the site of nbosomal RNA synthesis and the rlbosomal RNA genes are repeated lOO-SOO-tlmes/dlplold genome [ 1,2] It hds been estimated that the DNA content/nucleolus 1s 1 3 pg and that the DNA content/cell 1s 8 pg for Novlkoff rat cells [ 1 ] Rlbosomai DNA comprised 0 008% of the total DNA [3] and -0 05% of nucleoldr DNA The remaining 99 95% of nucleolar DNA has not yet been chdracterlzed Restriction endonuclease dIgestIon followed by gel electrophoresls has been used to detect repeated sequences m DNA from several mammahan species [4-61 Novlkoff rat hepatoma DNA was analyzed by gel electrophoresls after EcoRI restrIction endonuclease digestIon m this laboratory SrnallEcoRI fragments of Novlkoff rat DNA were exammed [7] by acrylamide gel electrophoresls and large EcuRI fragments of Novlkoff rat DNA [8] by agarose gel electrophorests The largest EcoRI fragment, fragment A, was reported [8] localized to the nucleolus Here, HlndIII digestIon patterns of total nuclear DNA, nucleolar DNA, and extranucleolar nucleoplasmlc DNA have been studied by agarose and acrylamlde gel electrophoresls From quantltatlve analysis of the amount of the smallest HzndIII DNA fragment m various fractions of the nucleus, this fragment has been found to be localized to the nucleolus 2 Materials and methods