USE OF ULTRAVIOLET-LIGHT IN THE FRACTIONATION OF CHROMATIN CONTAINING UNSUBSTITUTED AND BROMODEOXYURIDINE-SUBSTITUTED DNA

Two procedures are described for the fractionation of chronatin containing unsubstituted (LL) DNA and DNA unifilarly substituted with bromodeoxyuridine (a). The two procedures rely upon the sensitivity of bromodeoxyuridine-containing DNA to UV light to induce either strand hreakage or protein crosslinking. When a mixture of LL and a chromatin is irradiated with UV light, the a DNA fragments into molecules of smaller molecular weight than the I DNA and crosslinka more chromosomal protein than the LL DNA. LL and a chromatin can be fractionated on the basis of size by centrifuging through a neutral sucrose gradient. The a DNA-protein adducts that are generated by the UV light have a unique buoyant density and may be isolated by isopycnic centrifugation in cs2SO4 The ability to fractionate LL. and HL chromatin permits certain studies on the structure of replicating chromatin. © 1979 Information Retrieval Limited.