Characterization of mouse Taper liver tumor hepatoma chromatin autodigestion and the release of euchromatic segments

Abstract

Glycerol density gradient analysis of unsheared mouse Taper liver tumor hepatoma chromatin revealed that the nonpelletable (~20%) chromatin sedimented with a fairly uniform size distribution. Shearing of the chromatin by autodigestion in the presence of added Mg 2+ and Ca 2+ resulted in the release of chromatin segments (from the originally pelletable chromatin) with sedimentation chracteristics similar to those of the original nonpelletable chromatin. However, shearing of the chromatin by autodigestion in the absence of added Mg 2+ and Ca 2+ or by digestion with added micrococcal nuclease or by physical shearing (Virtis homogenization) resulted in the release of chromatin segments (from the originally pelletable chromatin) which did not display the same sedimentation characteristics. Divalent cation concentration, pH, and incubation temperature were all found to be important factors affecting the final results. Satellite DNA content analyses revealed that the chromatin segments released from the (initially) pelletable chromatin during the early stages of autodigestion (in the presence of added Mg 2+ and Ca 2+) were satellite DNA-deficient; at later times during the autodigestion, it appeared that satellite DNA-enriched segments were released from the (initially) pelletable chromatin. A model is proposed which attempts to explain the kinetics of autodigestion.