title: Refined requirements for protein regions important for activity of the TALE AvrBs3.
abstract: AvrBs3, the archetype of the family of transcription activator-like (TAL) effectors from phytopathogenic Xanthomonas bacteria, is translocated by the type III secretion system into the plant cell. AvrBs3 localizes to the plant cell nucleus and activates the transcription of target genes. Crucial for this is the central AvrBs3 region of 17.5 34-amino acid repeats that functions as a DNA-binding domain mediating recognition in a "one-repeat-to-one base pair" manner. Although AvrBs3 forms homodimers in the plant cell cytosol prior to nuclear import, it binds DNA as a monomer. Here, we show that complex formation of AvrBs3 proteins negatively affects their DNA-binding affinity in vitro. The conserved cysteine residues at position 30 of each repeat facilitate AvrBs3 complexes via disulfide bonds in vitro but are also required for the gene-inducing activity of the AvrBs3 monomer, i.e., activation of plant gene promoters. Our data suggest that the latter is due to a contribution to protein plasticity and that cysteine substitutions to alanine or serine result in a different DNA-binding mode. In addition, our studies revealed that extended parts of both the N-terminal and C-terminal regions of AvrBs3 contribute to DNA binding and, hence, gene-inducing activity in planta.
authors.affiliation: Institute for Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Tom
authors.initials: T
authors.lastname: Schreiber
authors.affiliation: Institute for Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Anika
authors.initials: A
authors.lastname: Sorgatz
authors.affiliation: Institute for Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany; European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, Hamburg, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: List
authors.affiliation: Institute for Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Doreen
authors.initials: D
authors.lastname: Blüher
authors.affiliation: Institute for Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Thieme
authors.affiliation: European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, Hamburg, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Wilmanns
authors.affiliation: Institute for Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Ulla
authors.initials: U
authors.lastname: Bonas
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018744:DNA, Plant / Q000378:metabolism; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014974:Xanthomonas / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D018744:DNA, Plant; D014157:Transcription Factors