title: Reversible phosphorylation of a nucleosome binding protein that stimulates transcription of nucleosome deoxyribonucleic acid.
abstract: A nonhistone chromosomal protein (D-55) of Mr 55000 has been isolated in homogeneous form from calf thymus by using the standard salt-extraction procedures for the isolation of nonhistone chromosomal proteins followed by hydroxyapatite chromatography. D-55 is further characterized as coming from the group of nonhistone chromosomal proteins easily phosphorylated by an endogenous nuclear protein kinase. The kinase incorporates 1 mol of phosphate per mol of protein from [gamma-32P]ATP. The unphosphorylated form of D-55 binds to DNA, histones, and nucleosomes. Phosphorylation of D-55 does not significantly alter the binding of D-55 to DNA but greatly enhances its binding to histones and nucleosomes. Binding of D-55 to reconstituted nucleosomes enhances transcription of the nucleosome DNA by E. coli RNA polymerase by approximately 100-fold, to a level approximately 4 times that observed with naked calf thymus DNA as template. Phosphorylation of D-55 abolishes this enhancement. Binding of D-55 produces no apparent alteration in nucleosome structure as assayed by nuclease digestion patterns. In contrast, phospho-D55 alters nucleosome structure significantly.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D002942:Circular Dichroism; D004247:DNA / Q000378:metabolism*; D024001:HMGN Proteins; D007700:Kinetics; D008970:Molecular Weight; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009707:Nucleosomes / Q000378:metabolism*; D010766:Phosphorylation; D013950:Thymus Gland / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D000596:Amino Acids; D002352:Carrier Proteins; D002868:Chromosomal Proteins, Non-Histone; D024001:HMGN Proteins; C028567:HMGN4 protein, human; D009707:Nucleosomes; D004247:DNA