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dictyNews Volume 27 Number 16
dictyNews
Electronic Edition
Volume 27, number 16
December 1, 2006
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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A 40.7 kDa Rpp30/Rpp1 homologue is a protein subunit of
Dictyostelium discoideum RNase P holoenzyme
Anastassios Vourekas1, Dimitra Kalavrizioti1, Ioannis K. Zarkadis2,
Georgios A. Spyroulias3, Constantinos Stathopoulos4 and Denis Drainas1
Departments of Biochemistry1 and Biology2, School of Medicine, University
of Patras, Patras 265 04, Greece. Department of Pharmacy3, University of
Patras, Patras 265 04, Greece
Department of Biochemistry and Biotechnology4, University of Thessaly,
Larissa 412 21, Greece
Biochimie, in press
RNase P is an essential and ubiquitous endonuclease that mediates the
maturation of the 5' ends of all precursor tRNA molecules. The holoenzyme
from Dictyostelium discoideum possesses RNA and protein subunits
essential for activity, but the exact composition of the ribonucleoprotein
complex is still under investigation. Bioinformatic analysis of D. discoideum
genome identified seven open reading frames encoding candidate RNase P
protein subunits. The gene named drpp30, encodes a protein with a
predicted molecular mass of 40.7 kDa that clusters with Rpp1 and Rpp30
RNase P protein subunits from Saccharomyces cerevisiae and human
respectively, which have significantly lower molecular masses. Cloning and
heterologous expression of DRpp30 followed by immunochemical analysis
of RNase P active fractions demonstrates its association with RNase P
holoenzyme. Furthermore, we show that DRpp30 can bind D. discoideum
RNase P RNA and tRNA transcripts in vitro, giving a first insight of its
possible role in D. discoideum RNase P function. Homology modelling using
as a template the archaeal Ph1887p, and molecular dynamics simulations
of the modeled structure suggest that DRpp30 adopts a TIM-barrel fold.
Submitted by Denis Drainas [Drainas@med.upatras.gr]
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Filamin regulated F-actin assembly is essential for morphogenesis and
controls phototaxis in Dictyostelium
Nandkumar Khaire, Rolf Mueller, Rosemarie Blau-Wasser, Ludwig Eichinger,
Michael Schleicher, Matthias Rief, Tad A. Holak, Angelika A. Noegel
Journal of Biological Chemistry, in press
Dictyostelium strains lacking the F-actin crosslinking protein filamin
(ddFLN) have a severe phototaxis defect at the multicellular slug stage.
Filamins are rod-shaped homodimers that cross-link the actin cytoskeleton
into highly viscous, orthogonal networks. Each monomer chain of filamin is
comprised of an F-actin-binding domain and a rod domain. In rescue
experiments only intact filamin re-established correct phototaxis in filamin
minus mutants whereas C-terminally truncated filamin proteins that had lost
the dimerisation domain and molecules lacking internal repeats but retaining
the dimerisation domain did not rescue the phototaxis defect. Deletion of
individual rod repeats also changed their subcellular localisation and mutant
filamins in general were less enriched at the cell cortex as compared to the
full length protein and were increasingly present in the cytoplasm. For
correct phototaxis ddFLN is only required at the tip of the slug as
expression under control of the cell type specific ecmA promoter and mixing
experiments with wild type cells supported phototactic orientation. Likewise,
in chimeric slugs wild type cells were primarily found at the tip of the slug
which acts as an organiser in Dictyostelium morphogenesis.
Submitted by: Angelika A. Noegel [noegel@uni-koeln.de]
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Induced symbiosis: Distinctive Escherichia coli-Dictyostelium discoideum
transferable co-cultures on agar
Masahiko Todoriki1, Itaru Urabe1
1Department of Biotechnology, Graduate School of Engineering, Osaka
University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
Email. riki3@bio.eng.osaka-u.ac.jp
Symbiosis, in press
Despite the near ubiquity of symbiosis, only a few new symbiotic
associations have been reported. The establishment of the unique
amoeba-bacterial symbiosis observed by Jeon and his colleagues has
been difficult to retrace experimentally mainly because of the failure to
grow both partners in pure culture. The details of symbiosis origin and
especially laboratory induction are unknown in all cases. Here, we present
an experiment in which specific strains of four-year subculture Escherichia
coli and Dictyostelium discoideum evolved interdependently to produce a
new morphological entity on agar plates. The cocultured organisms lost
their pure culture identities under the conditions in which both control
organisms retained their independent culturability. Between days 32 and
101 of culturing of E. coli and between days 259 and 645 in D. discoideum
pure culture identity was lost. Yet through the four years both organisms
could always be cocultured and stored frozen. We traced the emergence
of characteristic changes toward a repeatedly inducible symbiotic
relationship in pure cultures of both cocultured organisms. Since both the
enteric bacterium and the cellular slime mold are free-living and culturable
in pure culture, genetically well-characterized. We provide a useful model
for the laboratory study of symbiotic evolution.
Submitted by: Masahiko Todoriki [todoriki2004@yahoo.co.jp]
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[End dictyNews, volume 27, number 16]
