Based on solubility properties, the human myeloid cell nuclear differentiation antigen exists as at least two distinct populations. Most is easily extracted from isolated nuclei in 0.35 M NaCl, while 20 percent resists such treatment. Compared to undigested nuclei, both the amount of myeloid cell nuclear differentiation antigen (MNDA) released from nuclei after DNase I treatment and the amount resisting further extraction in 0.35 M NaCl increased after DNA was digested with DNase I. Under these conditions, there was a concomitant decrease in the amount of MNDA that was extractable with 0.35 M NaCl. Mixing nuclear protein extracts that contain MNDA with nuclei from cells that do not express this protein demonstrated that the MNDA redistributes from the freely soluble form to the nuclear residual fraction as a consequence of DNase I digestion. These data are consistent with a model in which the amount of MNDA that is tightly bound to salt-washed nuclei is held constant in the presence of an excess of unassociated MNDA in the nucleus, and that the level of MNDA binding to this nuclear fraction increases in proportion to the extent of DNA damage resulting from DNase I digestion.

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