Table I.

Phosphorylation by CKII of a synthetic peptide derived from the tobacco NR N-terminal acidic cluster

Peptide	Sequence	Concentration	Labeling
		μm	cpm
None	—	—	807
CKII substrate	RRREEETEEE	245	61,911
Acidic	SSSEDDDDDDEKNEG	300	12,529
	SSSEDDDDDDEKNEG	600	24,613

The in vitro phosphorylation by human CKII of a substrate peptide and of the peptide derived from the sequence of the tobacco NR N-terminal acidic cluster (acidic peptide) were compared. For details, see Methods. The possible phosphorylation sites for CKII are in bold type and are underlined.