Repressed and Active Chromatin Isolated From Interphase Lymphocytes

The compaction of mouse heterochromatin as studied by nuclease digestion

“…Sonication under the conditions in [6] led to a 4-5-fold enrichment of the satellite DNA in the pellet fraction ( fig. 1 c).…”

“…The classical procedure for the preparation of heterochromatin entails pretreatment of the nuclei in CaC12-containing buffer, swelling in sucrose, sonication, and differential centrifugation to obtain an insoluble heterochromatin fraction [6]. We attempted to replace sonication by nuclease treatment since sonication has been shown to harm the structure of chromatin [17], and chose micrococcal nuclease and DNase II for that purpose.…”

“…Prior to use, they were washed 3 times in 10 mM Tris-HC1 (pH 7.0), 3.3 mM CaC12 [6]. They were suspended in 0.25 M sucrose at 50 #g DNA/ml, allowed to stand on ice for 10 min and then sonicated, usually in 2-3 ml aliquots for 10 s in a Branson sonifier (S 125) using the microtip and the lowest setting.…”

“…The compact state ofheterochromatin has beenexploited as the basis for its biochemical isolation. By sonication of nuclei and differential centrifugation according to [6] a rapidly sedimenting fraction could be obtained from mouse, calf, and guinea pig liver nuclei which contained mostly satellite DNA [7][8][9].…”

Fractionation of plant chromatin with immobilized RNA‐polymerase

“…This can be achieved by different ways: centrifugation [3] ; ion exchange chromatography [4] ; or isopycnic centrifugation in an appropriate medium [6,7]. In our hands, fractionation by centrifugation on a linear density gradient of glycerol (7.5-75' gave satisfactory results buth this method is based rather on physical properties of nucleoproteins than on functional ones.…”