title: Phosphorylation of rat thymus histones, its control and the effects thereon of gamma-irradiation.
abstract: The phosphate content of rat thymus histones was determined. As expected for a replicating tissue, histones 1 and 2B were more phosphorylated and had higher 32P uptakes than did histones from resting liver nuclei; the other histones all showed 32P uptake, but the phosphate content and uptake of histone 2A was about half that for liver histone 2A. When thymus nuclei were incubated in a slightly hypo-osmotic medium, non-histone proteins and phosphorylated histones were released into solution; this was enhanced if ATP was present in the medium. [gamma-32P]ATP was incorporated into non-histone proteins, including protein P1, and into the ADP-ribosylated form of histone 1; negligible 32P was incprporated into the other, bound, histones. Histones 1 and 2B added to the incubation medium were extensively, and histones 2A and 4 slightly, phosphorylated. Histones released by increasing the ionic strength of the medium were phosphorylated. Added lysozyme and cytochrome c were neither bound nor phosphorylated, but added non-histone protein P1 was phosphorylated, causing other histones to be released from the nuclei, especially histones 2A and 3. The released histones were phosphorylated. gamma-Irradiation decreased 32P uptake into the non-ADP-ribosylated histones 1 and 4; phosphorylation of histone 1 in vitro was unaffected. The importance of non-histone proteins, ATP availability and nuclear protein kinases to the control of histone phosphorylation in vivo is discussed.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D005720:Gamma Rays; D006657:Histones / Q000378:metabolism*; D009113:Muramidase / Q000378:metabolism; D009994:Osmolar Concentration; D010710:Phosphates / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D013950:Thymus Gland / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D003574:Cytochrome c Group; D006657:Histones; D010710:Phosphates; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D009113:Muramidase