Cesium chloride density gradient sedimentation

The distribution of N and N was revealed by the technique of density-gradient equilibrium sedimentation. A small amount of DNA was dissolved in a concentrated solution of cesium chloride having a density close to that of the DNA (1.7 g This solution was centrifuged until it was nearly... 

In repair replication experiments, cells are irradiated and then incubated in medium containing 3H-5-bromodeoxyuridine ( H-BrdUrd). After a suitable repair period the cells are harvested, and the DNA is extracted and centrifuged to equilibrium in cesium chloride. When the gradient fractions are collected, it is possible to follow the new DNA (semiconservatively synthesized during repair and at hybrid density) by counts. The new DNA is half substituted with bromouracil (BrUra) and sediments to a lower point on the gradient than the old or parental DNA, which is detected by absorbancy at 260 nm or by incorporation of a second radioactive label and is, of course, not density labeled. The appearance of counts in the old DNA region is indicative that repair has occurred and that the new incorporation is truly in the parental... 

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