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dictyNews Volume 21 Number 06
Dicty News
Electronic Edition
Volume 21, number 6
August 29, 2003
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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Phosducin-like proteins in Dictyostelium discoideum: Implications for the
phosducin family of proteins
Mieke Blaauw, Jaco C. Knol, Arjan Kortholt, Jeroen Roelofs, Ruchira, Marten
Postma, Antonie J.W.G. Visser and Peter J.M. Van Haastert
Department of Biochemistry, University of Groningen, The Netherlands
EMBO Journal, in press
Retinal phosducin is known to sequester transducin Gbeta-gamma, thereby
modulating transducin activity. Phosducin is a member of a family of
phosducin-like proteins (PhLP) found in eukaryotes. Phylogeny of 33
phosducin-like proteins from metazoa, plants and lower eukaryotes
identified three distinct groups named phosducin-I to -III. We discovered
three phlp genes in Dictyostelium, each encoding a phosducin-like protein
of a different group. Disruption of the phlp1 gene strongly impaired G
protein signalling, apparently due to mislocalisation of Gbeta-gamma in
phlp1-null cells. GFP-Gbeta and GFP-G-gamma are membrane associated in
wild-type cells, but cytosolic in phlp1-null cells. Phlp2 disruption is
lethal due to a synchronous collapse of the cells after 16-17 cell
divisions. Phlp3 disruptants show no abnormal phenotype. These results
establish a role of phosducin-like proteins in facilitating folding,
localisation or function of proteins, in addition to modulating G protein
signalling.
Submitted by: P.J.M.van.Haastert [P.J.M.van.Haastert@chem.rug.nl]
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Roc, a Ras/GTPase domain in complex proteins
Leonard Bosgraaf and Peter J.M. Van Haastert
Department of Biochemistry, University of Groningen, The Netherlands
BBA, in press
We identified a novel group of the Ras/GTPase superfamily, termed Roc, that is
present as domain in complex proteins together with other domains, including
Leucine rich repeats, Ankyrin repeats, WD40 repeats, kinase domains, RasGEF
and RhoGAP domains. Roc is always succeeded by a novel 300-400 amino acids
long domain, termed COR. Proteins with Roc/COR are present in prokaryotes,
Dictyostelium, plant and metazoa.
Submitted by: P.J.M.van.Haastert [P.J.M.van.Haastert@chem.rug.nl]
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Chemoattractant-stimulated calcium influx in Dictyostelium discoideum does not
depend on cGMP
Douwe M. Veltman, Jan Sietse De Boer and Peter J.M. Van Haastert
Department of Biochemistry, University of Groningen, The Netherlands
BBA, in press
Chemoattractant stimulation of Dictyostelium cells leads to the opening of
calcium channels in the plasma membrane, causing extracellular calcium to flux
into the cell. The genetically uncharacterised mutants stmF and KI8 show
strongly altered chemoattractant stimulated cGMP responses. The aberrant
calcium influx in these strains has provided evidence that the chemoattractant
stimulated calcium influx is potentiated by cGMP. We have tested this
hypothesis in genetically defined mutants by measuring the calcium influx in a
strain that lacks intracellular cGMP due to the disruption of two guanylyl
cyclases, and in a strain with increased cGMP levels caused by the disruption
of two cGMP-degrading phosphodiesterases. The results reveal that the calcium
influx stimulated by cAMP or folic acid is essentially identical in these
strains. We conclude that cGMP is not involved in chemoattractant-stimulated
calcium influx.
Submitted by: P.J.M.van.Haastert [P.J.M.van.Haastert@chem.rug.nl]
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Temporal and Spatial Expression of Ammonium Transporter Genes During Growth and
Development of Dictyostelium discoideum.
Susan C. Follstaedt, Janet H. Kirsten, Charles K. Singleton.
Differentiation, in press
Ammonia is an important signaling molecule involved in the regulation of
development in Dictyostelium. During aggregation, ammonia gradients are
established, and the ammonia concentration in the immediate environment or
within a particular cell throughout development may vary. This is due to the
rate of cellular ammonia production, its rate of loss by evaporation to the
atmosphere or by diffusion into the substratum and perhaps to cellular
transport by ammonia transporters (AMTs). Recent efforts in genome sequencing
have identified three ammonia transporters in Dictyostelium. In addition to
physically altering the levels of ammonia within cells, the AMTs also may play
a role in ammonia signaling. As an initial step in identifying such a function,
the temporal and spatial expression of the three amt genes is examined. RT-PCR
demonstrates that each of the three amt mRNAs is present and relatively constant
throughout growth and development. The spatial expression of these three amt
genes is examined during multiple stages of Dictyostelium development using in
situ hybridization. A distinct and dynamic pattern of expression is seen for
the three genes. In general, amtA is expressed heavily in prestalk cells in a
dynamic way, while amtB and amtC are expressed in prespore regions consistently
throughout development. AmtC also is expressed in the most anterior tip of
fingers and slugs, corresponding to cells that mediate ammonia?s effect on the
choice between slug migration versus culmination. Indeed, amtC null cells have
a slugger phenotype, suggesting AmtC functions in the signaling pathway
underlying the mechanics of this choice.
Submitted by: Charles Singleton [charle.k.singleton@vanderbilt.edu]
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[End Dicty News, volume 21, number 6]
