TABLE 4.

Nucleotide specificity of the S. solfataricus protein kinase^a

Nucleotide	Phosphate incorporation into casein (% control) (n)
ATP	32 ± 5 (3)
ADP	70 ± 17 (3)
AMP	96 ± 4 (3)
GTP	50 ± 12 (3)
GDP	85 ± 14 (2)
PPi	96 ± 4 (2)

^aSamples of the DE-52 fraction, 12.5 μg each, were subjected to SDS-PAGE in gels containing copolymerized casein. The protein kinase was renatured within the gel, the gels were sectioned into individual lanes, and the lanes were incubated overnight with the indicated nucleotides at a concentration of 50 mM. Afterwards, the nonlabeled nucleotides were washed away and an in gel assay was performed using [γ-³²P]ATP. The gels were then washed free of [γ-³²P]ATP, and the incorporation of [³²P]phosphate into protein was determined by electronic autoradiography. Phosphorylation of casein by unlabeled phosphate from the nucleotide present during the overnight preincubation period should be manifested as an attenuation of [³²P]phosphate during the subsequent incubation with [γ-³²P]ATP. Shown are the levels of [³²P]radioactivity incorporated into casein relative to those for controls in which no nucleotide was present during preincubation. All values are averages of multiple (n) determinations ± standard errors.