title: Identification of amino acid substitutions that render the Arabidopsis cytokinin receptor histidine kinase AHK4 constitutively active.
abstract: In Arabidopsis, three genes (AHK2, AHK3 and AHK4/CRE1) encode histidine kinases (His-kinases), which serve as cytokinin receptors. To understand how the external cytokinin signal activates the His-kinase across the cell membrane, we exploited the power of microbial genetics to isolate several AHK4 mutants that function independently of cytokinin in both prokaryotic and eukaryotic assay systems. In each mutant, a single amino acid substitution within the second membrane-spanning segment, or within the region around the phosphorylation His site, renders the His-kinase constitutively active. These mutant receptors appear to have a 'locked-on' conformation, even in the absence of stimulus. We discuss the implications of these data for the structure and function of the cytokinin receptor His-kinases in plants.
authors.affiliation: Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University, Furocho, Chikusa-ku, Nagoya, Japan.
authors.forename: Kumiko
authors.initials: K
authors.lastname: Miwa
authors.forename: Kuniko
authors.initials: K
authors.lastname: Ishikawa
authors.forename: Kazunori
authors.initials: K
authors.lastname: Terada
authors.forename: Hisami
authors.initials: H
authors.lastname: Yamada
authors.forename: Tomomi
authors.initials: T
authors.lastname: Suzuki
authors.forename: Takafumi
authors.initials: T
authors.lastname: Yamashino
authors.forename: Takeshi
authors.initials: T
authors.lastname: Mizuno
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003583:Cytokinins / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D029681:Arabidopsis Proteins; D003583:Cytokinins; D011956:Receptors, Cell Surface; D011494:Protein Kinases; C421783:WOL protein, Arabidopsis