title: Sac3, an Snf1-like serine/threonine kinase that positively and negatively regulates the responses of Chlamydomonas to sulfur limitation.
abstract: The Sac3 gene product of Chlamydomonas positively and negatively regulates the responses of the cell to sulfur limitation. In wild-type cells, arylsulfatase activity is detected only during sulfur limitation. The sac3 mutant expresses arylsulfatase activity even when grown in nutrient-replete medium, which suggests that the Sac3 protein has a negative effect on the induction of arylsulfatase activity. In contrast to its effect on arylsulfatase activity, Sac3 positively regulates the high-affinity sulfate transport system-the sac3 mutant is unable to fully induce high-affinity sulfate transport during sulfur limitation. We have complemented the sac3 mutant and cloned a cDNA copy of the Sac3 gene. The deduced amino acid sequence of the Sac3 gene product is similar to the catalytic domain of the yeast Snf1 family of serine/threonine kinases and is therefore classified as a Snf1-related kinase (SnRK). Specifically, Sac3 falls within the SnRK2 subfamily of kinases from vascular plants. In addition to the 11 subdomains common to Snf1-like serine/threonine kinases, Sac3 and the plant kinases have two additional subdomains and a highly acidic C-terminal region. The role of Sac3 in the signal transduction system that regulates the responses of Chlamydomonas to sulfur limitation is discussed.
authors.affiliation: Department of Botany, 353 Bessey Hall, Iowa State University, Ames, Iowa 50011-1020, USA. jdavies@iastate.edu
authors.forename: J P
authors.initials: JP
authors.lastname: Davies
authors.forename: F H
authors.initials: FH
authors.lastname: Yildiz
authors.forename: A R
authors.initials: AR
authors.lastname: Grossman
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001192:Arylsulfatases / Q000378:metabolism; D020134:Catalytic Domain; D016825:Chlamydomonas reinhardtii / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D003470:Culture Media; D006706:Homeostasis; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics; D011110:Polymorphism, Genetic; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013455:Sulfur / Q000378:metabolism*
chemical_list: D003470:Culture Media; D010940:Plant Proteins; D013455:Sulfur; C120564:Sac3 protein kinase; D017346:Protein Serine-Threonine Kinases; D001192:Arylsulfatases