General Structure of AP-1 Subunits and Characteristics of the Jun Proteins
This chapter focuses primarily on the Jun proteins. In Jun proteins, the transactivation domain is located within the TV-terminal half of the protein while the DNA binding domains of Jun and the cyclic AMP (cAMP) response element binding factor/ATF are located at the C-terminus. In contrast to the transactivation domains, whose structural properties are poorly understood, a large body of information on the DNA binding domains of Jun, Fos, and other activator protein factors has been collected. The existence of a large number of possible combinations of partners would only by relevant physiologically if the individual dimers differed in DNA affinity or sequence specificity of the combined DNA binding domains of the subunits. In vivo mutation analysis of the Jun proteins has identified three subdomains that together form the transactivation domain. Considerable differences in selectivity and stability among the Basic leucine zipper proteins have been found with regard to dimerization.