Histones Phosphokinase

Imidazole (histidine) Phosphoglycerate mutase, succinyl-CoA synthetase, nucleoside diphosphokinase, histone phosphokinase, acid phosphokinase Phosphorylenzyme... 

His —f= Acid phosphokinase, histone phosphokinase, nucleoside diphosphokinase, phosphoglycerate mutase, succinyl- phosphorylenzyme... 

An energy-dependent histone phosphorylation was discovered in calf and rat thymus nuclei [68, 69], A histone phosphokinase has been purified from liver, and some of its properties have been studied. The kinase phosphorylates only the serine residues of histones or protamines. It is inactive on other proteins and therefore different from the typical phosphopro-tein kinase. In vitro the enzyme phosphorylates all histone fractions, but FI appears to be a preferred substrate. 

The hypothesis that it is not the presence or absence of histones, but their chemical modification (acetylation, methylation, phosphorylation) which determines the repressive or active (de-repressed) state of DNA has often been put forward. Phosphorylation of histones takes place through the action of the enzyme histone phosphokinase after synthesis of the histone protein molecule (with the formation of phosphoserine). Phosphorylation is most perceptible in the lysine-rich fraction. Conversely, acetylation of histones, determined by incorporation of labeled acetate, takes place most actively in arginine-rich histone, and a relationship exists... 

Lake, R. S., and Salzman, N. P., 1972, Occurrence and properties of a chromatin-associated Fl-histone phosphokinase in mitotic Chinese hamster cells. Biochemistry 11 4817. 

S ATP -I- [DNA-directed eukaryotic RNA polymerase II subunit Ila] (<4> distinct from other protein phosphokinases, transfers about 20 phosphates to the heptapeptide repeats Pro-Thr-Ser-Pro-Ser-Tyr-Ser in C-terminal domain of MW 220000 subunit of RNA-polymerase II [7] <4> substrates are RNA-polymerase II subunits of wheat germ, soy bean, pea and human [7] phosphorylates predominantly Ser-residues [1-3,5,7] <1> kinase CTDKl almost exclusively phosphorylates Ser-residues [5] <1> kinase CTDK2 phosphorylates to a lesser extent Thr-resi-dues [1] <3-5> phosphorylates to a lesser extent Thr-residues [1,5,7] <1> phosphorylates Ser- and Thr-residues equally [6] <1,3,5> phosphorylates not Tyr-residues [1,6] <1> kinase CTDKl 33 mol phosphate per mol IIA-subunit [5] <1> kinase CTDK2 40-50 mol phosphate per mol IIA-subunit, i.e. 1 phosphate per heptapeptide repeat [5] <4> no substrate is GTP [7] <2,4> no substrates are CTP and UTP [3,7] <2> no substrates are dTTP and AMP-PNP [3] <4> no substrates are bovine serum albumin and calf thymus histone [7] <5> no substrate is phosvitin... 

Typically, 1.5 pg plasmid DNA is incubated with embryo extract (3 mg protein) containing 30 mM creatine phosphate, 3 mM MgCl2,3 mM ATP (pH 8.0) 0.1 pg/ ml creatine phosphokinase (type 1, Sigma), 1 mM DTT, and EX buffer to a total volume of 200 /u.1. The conductivity of the assembly reaction mix is equivalent to 65 mM KCl. The reaction is carried out for up to 6 hr at 26°C. Preblastoderm embryo extracts contain a maternal stockpile of core histones that are utilized in the assembly reaction. The linker histone, HI, on the other hand, is absent from the early embryo and, hence, from the reconstituted chromatin. However, exogenous HI can be incorporated into chromatin during the assembly reaction, where it increases the nucleosome repeat length from 180 to 197 bp DNA (Becker and Wu, 1992). 

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See also in sourсe #XX -- [ ]

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