title: Crystal structure of the MATa1/MAT alpha 2 homeodomain heterodimer bound to DNA.
abstract: The Saccharomyces cerevisiae MATa1 and MAT alpha 2 homeodomain proteins, which play a role in determining yeast cell type, form a heterodimer that binds DNA and represses transcription in a cell type-specific manner. Whereas the alpha 2 and a1 proteins on their own have only modest affinity for DNA, the a1/alpha 2 heterodimer binds DNA with high specificity and affinity. The three-dimensional crystal structure of the a1/alpha 2 homeodomain heterodimer bound to DNA was determined at a resolution of 2.5 A. The a1 and alpha 2 homeodomains bind in a head-to-tail orientation, with heterodimer contacts mediated by a 16-residue tail located carboxyl-terminal to the alpha 2 homeodomain. This tail becomes ordered in the presence of a1, part of it forming a short amphipathic helix that packs against the a1 homeodomain between helices 1 and 2. A pronounced 60 degree bend is induced in the DNA, which makes possible protein-protein and protein-DNA contacts that could not take place in a straight DNA fragment. Complex formation mediated by flexible protein-recognition peptides attached to stably folded DNA binding domains may prove to be a general feature of the architecture of other classes of eukaryotic transcriptional regulators.
authors.affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205-2185, USA.
authors.forename: T
authors.initials: T
authors.lastname: Li
authors.forename: M R
authors.initials: MR
authors.lastname: Stark
authors.forename: A D
authors.initials: AD
authors.lastname: Johnson
authors.forename: C
authors.initials: C
authors.lastname: Wolberger
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D004271:DNA, Fungal / Q000737:chemistry* / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry* / Q000378:metabolism; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000378:metabolism; D006860:Hydrogen Bonding; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009875:Operator Regions, Genetic; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000737:chemistry* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D014158:Transcription, Genetic
chemical_list: D004271:DNA, Fungal; D005656:Fungal Proteins; D018398:Homeodomain Proteins; C096063:MATA1 protein, S cerevisiae; C062928:MATA2 protein, S cerevisiae; D046911:Macromolecular Substances; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins