Circular dichroism, thermal denaturation, and deoxyribonuclease I digestion studies of nucleosomes highly enriched in high mobility group proteins HMG 1 and HMG 2.
Salt-soluble (S) nucleosomes that contain near equimolar high mobility group nonhistone chromosomal proteins HMG 1 and HMG 2 and lack histone H1 were isolated from mouse myeloma nuclei. Comparisons of the sedimentation, near-UV circular dichroism, thermal denaturation, and pattern of DNase I digestion of S nucleosomes with these properties of nucleosome cores or "typical" nucleosomes containing H1 did not detect significant differences. These results indicate that HMG 1 and 2 do not affect the conformation and stability of nucleosomes or nucleosomal DNA and are consistent with the proposal that major functions of HMG 1 and 2 are to replace H1 and maintain the (micro) solubility and accessibility of local chromatin regions. In contrast to these similarities, the initial rate of DNase I digestion of S nucleosomes was approximately 3 times that of chromatin depleted in S nucleosomes. This is consistent with a relation of S nucleosomes to transcription and suggests that subtle factors (not necessarily HMG 1 and 2) determine DNase I susceptibility.
D000818:Animals; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D002868:Chromosomal Proteins, Non-Histone; D002942:Circular Dichroism; D003850:Deoxyribonuclease I; D003851:Deoxyribonucleases; D004720:Endonucleases; D006609:High Mobility Group Proteins; D006358:Hot Temperature; D051379:Mice; D009691:Nucleic Acid Denaturation; D009707:Nucleosomes / Q000032:analysis*; D011489:Protein Denaturation; D013056:Spectrophotometry, Ultraviolet
D002868:Chromosomal Proteins, Non-Histone; D006609:High Mobility Group Proteins; D009707:Nucleosomes; D003851:Deoxyribonucleases; D004720:Endonucleases; D003850:Deoxyribonuclease I