Affinity labeling of Avena phytochrome with ATP analogs.
The presence of ATP-dependent, polycation-stimulated protein kinase activity in highly purified phytochrome preparations [Wong, Y.-S., Cheng, H.-C., Walsh, D. A. & Lagarias, J. C. (1986) J. Biol. Chem. 261, 12089-12097] has renewed the hypothesis that the phytochrome photoreceptor possesses enzymatic activity. A prerequisite for protein kinase function is the presence of an ATP binding site. Here we present evidence for a nucleoside triphosphate binding site(s) in the phytochrome molecule. Two ATP analogs, 5'-p-fluorosulfonylbenzoyladenosine and 8-azidoadenosine 5'-triphosphate, were used to affinity label purified Avena phytochrome. Labeling with both reagents is stimulated by the polycations poly(Lys(75),Ala(25)) and histone H1. Coincubation with ATP inhibits the polycation-stimulated labeling of phytochrome. In similar experiments GTP, CTP, UTP, ADP, and pyrophosphate, but not adenosine or AMP, also prevent photoaffinity labeling of phytochrome.
Department of Biochemistry and Biophysics, University of California, Davis, CA 95616.
Y S
YS
Wong
J C
JC
Lagarias