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Calcium-dependent ADP-ribosylation of high-mobility-group I (HMGI) proteins
V Giancotti1, A Bandiera, C Sindici
1Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, Università di Trieste, Italy.
Abstract:
Micrococcal nuclease digestion of nuclei from mouse Lewis lung carcinoma cells releases a protein mixture into the supernatant that lacks histone H1 and contains a full complement of high-mobility-group I (HMGI) proteins (i.e. I, Y and I-C). This implies that all three HMGI proteins are localized at the nuclease-sensitive regions of active chromatin. It is also shown that if Ca2+ ions are present in the nuclear incubation buffer (with or without exogenous nuclease), all three HMGI proteins become ADP-ribosylated. We propose that this modification of HMGI family proteins is part of the general poly(ADP-ribosyl)ation that accompanies DNA damage in apoptosis and other processes.
Insights
High-mobility-group I (HMGI) proteins are found in active chromatin regions. In the presence of calcium ions, these HMGI proteins undergo ADP-ribosylation, a modification linked to DNA damage.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- High-mobility-group I (HMGI) proteins are architectural factors involved in chromatin structure.
- Understanding the localization and modification of HMGI proteins is crucial for comprehending gene regulation and DNA repair.
- Lewis lung carcinoma cells provide a model system to study nuclear protein dynamics.
Purpose of the Study:
- To investigate the localization of high-mobility-group I (HMGI) proteins within the nucleus.
- To determine if HMGI proteins are modified by ADP-ribosylation under specific conditions.
- To explore the potential role of HMGI modification in cellular processes involving DNA damage.
Main Methods:
- Micrococcal nuclease digestion of isolated nuclei from mouse Lewis lung carcinoma cells.
- Fractionation of released proteins via supernatant collection.
- Analysis of protein composition using biochemical assays.
- Induction of ADP-ribosylation using calcium ions (Ca2+) in nuclear incubation buffers.
Main Results:
- Micrococcal nuclease digestion released proteins lacking histone H1 but containing all three HMGI proteins (I, Y, and I-C).
- This indicates HMGI proteins are located in nuclease-sensitive regions of active chromatin.
- The presence of Ca2+ ions induced ADP-ribosylation of all three HMGI proteins, irrespective of nuclease presence.
Conclusions:
- HMGI proteins are localized to active chromatin regions sensitive to nuclease digestion.
- HMGI proteins are substrates for ADP-ribosylation in the presence of calcium ions.
- This ADP-ribosylation of HMGI proteins may be associated with DNA damage responses, including apoptosis.