Intranuclear distribution of 2,2',4,4',5,5'-hexachlorobiphenyl and 2,3,7,8,-tetrachlorodibenzo-p-dioxin

The in vitro intranuclear distribution of the chlorinated aromatic hydrocarbon compounds 2,2',4,4',5,5'-hexachlorobiphenyl and 2,3,7,8-tetrachlorodibenzo-p-dioxin was determined in isolated rat liver cell nuclei. Suspended nuclei were incubated with the 3H-labeled congeners, and the incubation terminated by brief UV irradiation. High-intensity UV irradiation at 254 nm changes the reversible association between macromolecules and ligands into covalent linkages and thus stabilizes the equilibrium distribution. The nuclei were then fractionated with the radioactive congeners covalently linked to the purified fractions. The intranuclear distribution of the model compounds was not uniform. The majority of either chemical was attached to the nuclear envelope and to the chromatin fraction. Much lower amounts were bound to nucleoli. The nuclear matrix was almost devoid of the chemicals. Minute amounts of either compound were detected in association with DNA, none with nuclear RNA. The substantial association of these chlorinated hydrocarbon model compounds with chromatin may bear more general biological relevance and point to detrimental effects on the genetic apparatus. The presented method yields an unequivocal profile of the genuine nuclear distribution of photoactivatable chemicals.