Dicty News Electronic Edition Volume 18, number 7 May 11, 2002 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu. Back issues of Dicty-News, the Dicty Reference database and other useful information is available at DictyBase--http://dictybase.org. ============= Abstracts ============= Evolutionary Analyses of the ABC transporters of Dictyostelium Christophe Anjard, the Dictyostelium Sequencing Consortium, and William F. Loomis Center for Molecular Genetics, Division of Biology, University of California San Diego, La Jolla, CA 92093-0368 Eukaryotic Cell, in press Summary The ABC super-family of genes is one of the largest in the genomes of both bacteria and eukaryotes. The proteins they encode all carry a characteristic 200-250 amino acid long ATP-Binding Cassette that gives them their family name. In bacteria they are mostly involved in nutrient import while in eukaryotes many are involved in export. Seven different families have been defined in eukaryotes based on sequence homology, domain topology and function. While only 6 ABC genes have been previously studied in detail in Dictyostelium discoideum, sequences from the well-advanced Dictyostelium genome project have allowed us to recognize 68 members of this super-family. They have been classified and compared to animal, plant and yeast orthologs to gain some insight on the evolution of this super-family. It appears that many of the genes inferred to have been present in the ancestor of the crown organisms duplicated extensively in some but not all phyla while others were lost in one lineage or the other. ----------------------------------------------------------------------------- Crystal structure of the motor domain of a class-I myosin Martin Kollmar, Ulrike Drrwang, Werner Kliche, Dietmar J. Manstein and F. Jon Kull Department of Biophysics, Max Planck Institute for Medical Research, Jahnstrae 29, 69120 Heidelberg, Germany EMBO J., in press The crystal structure of the motor domain of Dictyostelium discoideum myosin-IE, a monomeric unconventional myosin, was determined. The crystallographic asymmetric unit contains four independently resolved molecules, highlighting regions that undergo large conformational changes. Differences are particularly pronounced in the actin binding region and the converter domain. The changes in position of the converter domain reflect movements both parallel to and perpendicular to the actin axis. The orientation of the converter domain is ~30 more Rup than other myosin structures, indicating MyoE can produce a larger power stroke by rotating its lever arm through a larger angle. The role of extended loops near the actin-binding site is discussed in the context of cellular localization. The core regions of the motor domain are similar, and the structure reveals how that core is stabilized in the absence of an N-terminal SH3-like domain. ----------------------------------------------------------------------------- A role for YakA, cAMP and PKA in the regulation of stress responses of Dictyostelium discoideum cells. Alexandre Taminato#, Raquel Bagattini#, Renata Gorjo#, Guokai Chen*, Adam Kuspa* and Glaucia Mendes Souza#+. #Instituto de Qumica, Dep. Bioqumica, Universidade de So Paulo, Brazil. * Dep. Biochemistry and Molecular Biology, Baylor College of Medicine Houston, Texas, USA. + To whom correspondence should be sent. glmsouza@iq.usp.br FAX: 011-55-11-3815-5579 Phone: 011-55-11-3091-3815 Molecular Biology of the Cell (in press). Abstract The Dictyostelium protein kinase YakA is required for the growth to development transition. During growth YakA controls the cell cycle, regulating the intervals between cell divisions. When starved for nutrients Dictyostelium cells arrest growth and undergo changes in gene expression, decreasing vegetative mRNAs and inducing the expression of pkaC. YakA is an effector of these changes, being necessary for the decrease of vegetative mRNA expression and the increase of PKA activity that will ultimately regulate expression of adenylyl cyclase, cAMP synthesis and the induction of development. We report a role for this kinase in the response to nitrosoative or oxidative stress of Dictyostelium cells. Hydrogen peroxide and sodium nitroprusside arrest the growth of cells and trigger cAMP synthesis and activation of PKA in a manner similar to the well established response to nutrient starvation. We have found that yakA null cells are hyper sensitive to nitrosoative/oxidative stress and that a second-site mutation in pkaC suppresses this sensitivity. The response to different stresses has been investigated and YakA, cAMP and PKA have been identified as components of the pathway that regulate the growth arrest that follows treatment with compounds that generate reactive oxygen species. The effect of different types of stress was evaluated in Dictyostelium and the YakA/PKA pathway was also implicated in the response to heat stress. ----------------------------------------------------------------------------- Loss of the beta-catenin homologue aardvark causes ectopic stalk formation in Dictyostelium. Juliet C. Coates1, Mark J. Grimson2, Robin S. B. Williams1, Wayland Bergman1, Richard L. Blanton2 and Adrian J. Harwood1. 1 MRC Laboratory for Molecular Cell Biology, University College London, Gower Street, London WC1E 6BT, UK. 2 Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409, USA. Mechanisms of Development (in press) Abstract Aardvark (Aar) is a Dictyostelium b-catenin homologue with both cytoskeletal and signal transduction roles during development. Here, we show that loss of aar causes a novel phenotype where multiple stalks appear during late development. Ectopic stalks are preceded by misexpression of the stalk marker ST-lacZ in the surrounding tissue. This process does not involve the kinase GSK-3. Mixing experiments show that ectopic ST-lacZ expression and stalk formation is cell non-autonomous. The protein-cellulose matrix surrounding the stalk of aar mutant fruiting bodies is defective, and damage to the stalk of wild type fruiting bodies leads to ectopic ST-lacZ expression. We postulate that poor synthesis of the stalk tube matrix allows diffusion of a stalk cell-inducing factor into the surrounding tissue. ----------------------------------------------------------------------------- [End Dicty News, volume 18, number 7]