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dictyNews Volume 29 Number 11
dictyNews
Electronic Edition
Volume 29, number 11
October 12, 2007
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of dictyNews, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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Isoprenylcysteine carboxyl methylation is essential for development
in Dictyostelium discoideum
Ying Chen*, Kyle J. McQuade*, Xiao-Juan Guan, Peter A. Thomason,
Michael S. Wert, Jeffry B. Stock, Edward C. Cox**
Department of Molecular Biology, Princeton University, Princeton,
New Jersey 08544, USA
*These authors contributed equally to this work.
**To whom correspondence should be addressed (ecox@molbio.princeton.edu).
Molecular Biology of the Cell, in press
Members of the Ras superfamily of small GTPases and the heterotrimeric G
protein γ subunit are methylated on their carboxy-terminal cysteine residues
by isoprenylcysteine methyltransferase. In Dictyostelium discoideum, small
GTPase methylation occurs seconds after stimulation of starving cells by
cAMP and returns quickly to basal levels, suggesting an important role in
cAMP-dependent signaling. Deleting the isoprenylcysteine
methyltransferase-encoding gene causes dramatic defects. Starving mutant
cells do not propagate cAMP waves in a sustained fashion and do not aggregate.
Motility is rescued when cells are pulsed with exogenous cAMP, or co-plated
with wild-type cells, but the rescued cells exhibit altered polarity.
cAMP-pulsed methyltransferase-deficient cells that have aggregated fail to
differentiate, but mutant cells plated in a wild-type background are able
to do so. Localization of and signaling by RasG is altered in the mutant.
Localization of the heterotrimeric Ggamma protein subunit was normal, but
signaling was altered in mutant cells. These data indicate that
isoprenylcysteine methylation is required for intercellular signaling and
development in Dictyostelium.
Submitted by: Ted Cox [ecox@molbio.princeton.edu]
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An unusually low microsatellite mutation rate in Dictyostelium discoideum,
an organism with unusually abundant microsatellites
Ryan McConnell, Sara Middlemist, Clea Scala, Joan E. Strassmann,
David C. Queller
Dept. of Ecology and Evolutionary Biology, Rice University, Houston,
Texas, USA
Genetics, in press
The genome of the social amoeba Dictyostelium discoideum is known to have
a very high density of microsatellite repeats, including thousands of
triplet microsatellite repeats in coding regions that apparently code for
long runs of single amino acids. We used a mutation accumulation study
to see if unusually high microsatellite mutation rates contribute to this
pattern. There was a modest bias towards mutations that increase repeat
number, but because upward mutations were smaller than downward ones,
this did not lead to a net average increase in size. Longer
microsatellites had higher mutation rates than shorter ones, but did not
show greater directional bias. The most striking finding is that the
overall mutation rate is the lowest reported for microsatellites, about
1 x 10-6 for 10 dinucleotide loci and 6 x 10-6 for 52 trinucleotide loci
(which were longer). High microsatellite mutation rates therefore do
not explain the high incidence of microsatellites. The causal relation
may in fact be reversed, with low mutation rates evolving to protect
against deleterious fitness effects of mutation at the numerous
microsatellites.
Submitted by: Dave Queller [queller@rice.edu]
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[End dictyNews, volume 29, number 11]
