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Inhibition of apoptosis in stage A Chronic Lymphocytic Leukemia is reversed by acyclovir
No full textThe organization of repeated DNA sequences in the human genome
No full textThe arrangement of repetitive and non-repetitive DNA sequences was studied in the human genome. By Ag+-Cs2SO4 density gradient centrifugations of human DNA at different fragment size reannealed to different Cot values and c-RNA hybridization experiments, we have shown the presence of two repetitive DNA fractions, called fast and slow intermediate DNA, with different pattern of sequence organization. The fast intermediate DNA sequences (6% of the genome; CsCl density in renatured form: 1.703 g/ml) are in part clustered in fragments greater than 24,000 nucleotide pairs and in part in fragments ranging from 1,800 to 600 nucleotide pairs spaced with longer more complex sequences. The slow intermediate DNA sequences (30% of the genome; CsCl density in renatured form: 1.707 g/ml) appear to be finely interspersed with non-repetitive sequences. At a DNA fragment size of 600 nucleotide pairs only a third of the slow intermediate DNA sequences are free of unique sequences, while the other two thirds are still organized with unique sequences. It has also been shown that a great amount of the repetitive DNA sequence transcripts in heterogeneous nuclear RNA of HeLa cells are complementary to slow intermediate DNA sequences
Repeated sequences in human DNA
No full textHuman DNA has been fractionated in Ag+Cs2SO4 and Hg2+Cs2SO4 preparative density gradients, and the fractions obtained have been centrifuged in neutral CsCl after extensive dialysis to eliminate Hg2+ and Ag2+. By centrifugation in Ag+Cs2SO4 a new satellite, called satellite DNA II, has been isolated from human DNA. It has a density of 1.693 g/ml. in neutral CsCl, accounts for 2% of the total approximately, renatures rapidly and separates into complementary strands having different densities in alkaline CsCl. In Hg2+Cs2SO4 gradients human DNA appears to be composed of two classes of molecules. The first, which accounts for approximately 80% of the total, is highly heterogeneous in base composition, its density in CsCl ranging from 1.690 to 1.720 g/ml., and is distributed in Hg2+Cs2SO4 so that the A·T-rich fractions are on the heavy side and the G·C-rich fractions on the light side, as expected on the basis of the preferential binding of Hg2+ to A·T pairs. The second class, which accounts for approximately 15% of the total, is more homogeneous, has a density of 1.696 g/ml., and is located on the light side of the DNA band in the Hg2+Cs2SO4 gradient. This suggests that the amount of Hg2+ bound to this A·T-rich DNA is abnormally low. This second class of DNA has been isolated by preparative CsCl centrifugation from a pool of the light fractions obtained from DNA-Hg2+Cs2SO4 centrifugation. It tends to renature after heat-denaturation, as shown by the shift of its density towards the native value in neutral CsCl
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