Combinatoial CREB/ATF dimers and cellular growth control

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APPLICANT'S DESCRIPTION: Proteins of the ATF/CREB/AP-1 family are components of signal transduction pathways that monitor intracellular and extracellular conditions and transmit those signals to downstream targets. Some family members (e.g., vFos and vJun) are oncogenic. ATF/CREB/AP-1 proteins share a conserved bZIP domain that mediates both protein dimerization and sequence-specific DNA binding activity. While the bZIP domains are highly homologous to one another, some combinations of bZIP proteins form dimers, while others do not. Furthermore, different bZIP dimers have the remarkable ability to discriminate between closely related DNA binding sites. This enables a limited set of bZIP monomers to form a repertoire of heterodimers, each of which presumably regulates the expression of a specific set of genes involved in a particular biological response. An understanding of which bZIP protein dimers can form, what DNA sites they occupy, and how such events are regulated will reveal fundamental aspects in the control of cellular homeostasis and/or differentiation. The fission yeast S. pombe provides an attractive model organism for such a study. We have shown that bZIP proteins of fission yeast form combinatorial dimers in vivo and in vitro. The various dimers are under control of a MAP kinase cascade and different dimers elicit distinct effector functions. Because S. pombe has a small genome (about 6,000 genes), and the sequencing project is nearly complete, one can identify and analyze the majority of cellular bZIP proteins. Since mutants lacking bZIP proteins and signal transduction proteins are generally viable, it is also possible to reveal both upstream regulatory and downstream effector functions. A comprehensive and systematic analysis of bZIP protein dimers of fission yeast is proposed. Aim 1, To elucidate the bZIP alphabet of S. pombe: determine pairwise combinatorial associations of bZIP dimers and identify DNA sites to which they bind with high affinity. Aim 2, To reveal molecular determinants of combinatorial dimer formation and DNA binding: compare high-resolution structures of bZIP dimers alone and complexed to their DNA sites. Aim 3, To further characterize regulatory mechanisms for stress responses mediated by the Mts1 bZIP protein: elucidate the role of the MAP kinase Spcl in controlling an autoinhibitory function of Mts1.