How MAP Kinases Are Regulated

The ultraviolet (UV) response of mammalian cells is characterized by a rapid and selective increase in gene expression mediated by AP-1 and NF-kappa B. The effect on AP-1 transcriptional activity results, in part, from enhanced phosphorylation of the c-Jun NH2-terminal activation domain. Here, we describe the molecular cloning and characterization of JNK1, a distant relative of the MAP kinase group that is activated by dual phosphorylation at Thr and Tyr during the UV response. Significantly, Ha-Ras partially activates JNK1 and potentiates the activation caused by UV. JNK1 binds to the c-Jun transactivation domain and phosphorylates it on Ser-63 and Ser-73. Thus, JNK1 is a component of a novel signal transduction pathway that is activated by oncoproteins and UV irradiation. These properties indicate that JNK1 activation may play an important role in tumor promotion.

The crystal structure of the catalytic subunit of cyclic adenosine monophosphate-dependent protein kinase complexed with a 20-amino acid substrate analog inhibitor has been solved and partially refined at 2.7 A resolution to an R factor of 0.212. The magnesium adenosine triphosphate (MgATP) binding site was located by difference Fourier synthesis. The enzyme structure is bilobal with a deep cleft between the lobes. The cleft is filled by MgATP and a portion of the inhibitor peptide. The smaller lobe, consisting mostly of amino-terminal sequence, is associated with nucleotide binding, and its largely antiparallel beta sheet architecture constitutes an unusual nucleotide binding motif. The larger lobe is dominated by helical structure with a single beta sheet at the domain interface. This lobe is primarily involved in peptide binding and catalysis. Residues 40 through 280 constitute a conserved catalytic core that is shared by more than 100 protein kinases. Most of the invariant amino acids in this conserved catalytic core are clustered at the sites of nucleotide binding and catalysis.