Phosphorylation state and DNA-binding activity of c-Jun depend on the intracellular concentration of binding sites.

The DNA-binding activity of c-Jun expressed in eukaryotic cells was found to be markedly enhanced if the intracellular concentration of binding sites for this transcription factor was increased by cotransfection of specific plasmid DNA. Dephosphorylation experiments, phosphate mapping studies, and mutational analysis indicate that phosphorylation of a cluster of serine and threonine residues situated in close proximity to the DNA-binding domain is responsible for the observed adaptation of c-Jun activity to the intracellular concentration of accessible target sites.