title: Proton NMR investigation of the nucleosome core particle: evidence for regions of altered hydrogen bonding.
abstract: Novel 1H nuclear magnetic resonance (NMR) resonances, arising from exchangeable protons and centered at approximately 11.2 and 10.1 parts per million (ppm), have been observed in the low-field spectrum (10-15 ppm) of the chicken erythrocyte core particle [145 +/- 2 base pairs (bp)]. These peaks are located upfield from the normal adenine-thymine (A-T) and guanine-cytosine (G-C) imino peaks characteristic of B-form deoxyribonucleic acid (DNA) and are not observed in free DNA under identical conditions. The appearance of the new peaks is ionic strength dependent and temperature-reversible below 75 degrees C. At 25 degrees C, the upfield peak area represents 5% of the DNA base pairs (7 bp), while between 45 and 55 degrees C, the area increases to 18%, affecting approximately 25 bp. Area increases in the upfield resonances result in a complementary decrease in the A-T and G-C imino peaks found between 12 and 14 ppm. We believe these novel proton signals represent a histone-induced DNA conformational change which involves localized alteration of base pairing in the core particle.
mesh_terms: D000818:Animals; D002417:Cattle; D002645:Chickens; D004247:DNA / Q000032:analysis; D004912:Erythrocytes / Q000648:ultrastructure; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009707:Nucleosomes / Q000648:ultrastructure*; D013950:Thymus Gland
chemical_list: D009707:Nucleosomes; D004247:DNA