Cross-species annotation of basic leucine zipper factor interactions: Insight into the evolution of closed interaction networks.

Dimeric basic leucine zipper (bZIP) factors constitute one of the most important classes of enhancer-type transcription factors. In vertebrates, bZIP factors are involved in many cellular processes, including cell survival, learning and memory, cancer progression, lipid metabolism, and a variety of developmental processes. These factors have the ability to homodimerize and heterodimerize in a specific and predictable manner, resulting in hundreds of dimers with unique effects on transcription. In recent years, several studies have described dimerization preferences for bZIP factors from different species, including Homo sapiens, Drosophila melanogaster, Arabidopsis thaliana, and Saccharomyces cerevisiae. Here, these findings are summarized as novel, graphical representations of closed, interacting protein networks. These representations combine phylogenetic information, DNA-binding properties, and dimerization preference. Beyond summarizing bZIP dimerization preferences within selected species, we have included annotation for a solitary bZIP factor found in the primitive eukaryote, Giardia lamblia, a possible evolutionary precursor to the complex networks of bZIP factors encoded by other genomes. Finally, we discuss the fundamental similarities and differences between dimerization networks within the context of bZIP factor evolution.