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dictyNews Volume 18 Number 07
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.
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Abstracts
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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.
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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.
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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.
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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.
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[End Dicty News, volume 18, number 7]
