Activation of the endogenous proviral genes in mouse cells is not followed by increased sensitivity to deoxyribonuclease I digestion.

The disposition of chromosome proteins about the endogenous proviral DNA of BALB-c mouse has been studied. The sensitivity of the endogenous proviral DNA sequences to deoxyribonuclease I (DNaseI) was analysed in BALB-c mouse tissues (liver and spleen) and in the cell line JLS-V9 which does not produce virus. On all of these preparations the endogenous proviral DNA was as sensitive to DNase I digestion as total chromatin. Since the proviral genes in JLS-V9 cells were silent, it was of interest to study possible changes in the chromatin structure following virus induction by iododeoxyuridine. We could not detect any increase in the sensitivity of the endogenous proviral DNA to DNase I digestion following induction. The induction was very efficient, however, since 60% of the cells responded to produce intracellular virus antigens.