Recent studies have detailed the ability of activating transcription factor-2 (ATF-2) to mediate adenoviral E1a stimulation of gene expression; however, an endogenous regulator for the transcriptional activity of this protein has not been described. To characterize the regulation of ATF-2 activity, we have expressed full-length and truncated peptides corresponding to various regions of the ATF-2 protein in bacteria and the baculovirus insect cell system. Bacterially expressed truncated (350-505) but not full-length ATF-2, was able to bind a consensus cAMP response element-containing oligonucleotide, suggesting the N-terminal moiety may serve as a negative regulator of DNA-binding activity. In contrast, the full-length ATF-2 protein expressed in Spodoptera frugiperda (Sf9) cells using a recombinant baculovirus was fully competent to bind DNA. Protein phosphatase 2A reversed the DNA-binding activity by dephosphorylating the ATF-2 polypeptide. Microtubule-associated protein kinase catalyzed the phosphorylation and stimulated the DNA-binding activity of bacterially expressed full-length ATF-2. Phosphopeptide mapping of phosphorylated ATF-2 proteins identified a single peptide in the N-terminal moiety of ATF-2 phosphorylated by p42 or p54 microtubule-associated protein kinase. Therefore, we propose that phosphorylation of this regulatory site is sufficient to induce an allosteric structural change in the ATF-2 protein, which allows dimerization and subsequent DNA binding.