CALCIUM-DEPENDENT ADP-RIBOSYLATION OF HIGH-MOBILITY-GROUP-I (HMGI) PROTEINS

Micrococcal nuclease digestion of nuclei from mouse Lewis lung carcino ma cells releases a protein mixture into the supernatant that lacks hi stone I-Il and contains a full complement of high-mobility-group I (HM GI) proteins (i.e. I, Y and I-C). This implies that all three HMGI pro teins are localized at the nuclease-sensitive regions of active chroma tin. It is also shown that if Ca2+ ions are present in the nuclear inc ubation buffer (with or without exogenous nuclease), all three HMGI pr oteins become ADP-ribosylated. We propose that this modification of HM GI family proteins is part of the general poly(ADP-ribosyl)ation that accompanies DNA damage in apoptosis and other processes.