The high mobility group proteins and transcribed nucleosomes

Area of Science:

• Molecular Biology
• Chromatin Biology
• Nucleosome Structure

Background:

• Monomer nucleosomes are released from nuclei following micrococcal nuclease digestion.
• These released nucleosomes are known to be enriched in transcribed DNA sequences.
• Previous studies indicated a depletion of histone H1 and enrichment of high mobility group (HMG) proteins in these nucleosomes.

Purpose of the Study:

• To characterize the protein composition of monomer nucleosomes released from nuclei.
• To investigate the heterogeneity of these nucleosomes using polyacrylamide gel electrophoresis.
• To determine if HMG-nucleosomes are specifically enriched in transcribed DNA sequences.

Main Methods:

• Micrococcal nuclease digestion of nuclei to release monomer nucleosomes.
• Analysis of nucleosome protein composition, focusing on H1 and HMG proteins (HMG14, HMG17).
• Separation of nucleosomes by polyacrylamide gel electrophoresis (PAGE).

Main Results:

• Released monomer nucleosomes were depleted in H1 and enriched in HMG14, HMG17, and another HMG-like protein.
• PAGE analysis revealed heterogeneity among the released nucleosomes.
• Nucleosomes containing HMG14 and HMG17 were identified.
• However, HMG-nucleosomes from chick erythrocytes did not show enrichment in globin sequences.

Conclusions:

• Monomer nucleosomes released by nuclease digestion are distinct in protein composition, containing specific HMG proteins.
• Nucleosome heterogeneity exists, with distinct populations binding HMG proteins.
• The lack of globin sequence enrichment in HMG-nucleosomes suggests potential protein rearrangement or selective association.