Phosphorylation of tyrosine residues of RNA polymerase II and other nuclear proteins by active chromatin tyrosine kinase(s).
We demonstrate here for the first time that protein tyrosine kinases are present in the active chromatin of nucleus. The presence of tyrosine kinase activity in the active chromatin was initially determined using poly (Glu,Na-Tyr;4:1) (PGT) as a tyrosine phosphorylatable substrate. Active chromatin in the presence of cofactors phosphorylated PGT at a rate of 40 pmol/min. The phosphorylation of PGT by active chromatin was inhibited by 41, 47 and approximately 95% with genistein, n-ethylmaleimide and quercetin (known inhibitors of tyrosine kinases), respectively. A Lineweaver-Burk plot revealed an apparent Km of 50 micrograms/ml and Vmax of 45 pmol/min for active chromatin tyrosine kinase(s). Analyses of phosphorylation of endogenous substrates by immunoprecipitation, western blotting and phosphoamino acids revealed that active chromatin protein tyrosine kinase(s) are able to phosphorylate tyrosine residues of the large subunit of RNA pol II and several other active chromatin proteins. The ability of AC-PTKs to phosphorylate many proteins of active chromatin components argues strongly for its role(s) in regulating transcription.
Palangat
M
M
Department of Environmental Health Sciences, University of Alabama, Birmingham 35294, USA.
Roy
D
D
D000818:Animals; D002843:Chromatin / Q000378:metabolism*; D006224:Cricetinae; D008297:Male; D008647:Mesocricetus; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*
D002843:Chromatin; D009687:Nuclear Proteins; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D012319:RNA Polymerase II