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dictyNews Volume 24 Number 16
Dicty News
Electronic Edition
Volume 24, number 16
June 17, 2005
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 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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The Phosducin-like Protein Phlp1 is Essential for Gbeta-gamma Dimer
Formation in Dictyostelium
Jaco C. Knol1,3, Ruchira Engel2,3, Mieke Blaauw1, Antonie J.W.G. Visser2
and Peter J.M. van Haastert1
1Department of Biochemistry, University of Groningen, Nijenborgh 4,
9747 AG Groningen, The Netherlands and 2MicroSpectroscopy Centre,
Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703
HA Wageningen, The Netherlands 3 These authors contributed equally to
this work
Molecular and Cellular Biology, in press
Phosducin proteins are known to inhibit G protein-mediated signalling by
sequestering Gbeta-gamma subunits. However, Dictyostelium cells lacking
the phosducin-like protein PhLP1 display defective rather than enhanced
G protein signalling. Here we show that GFP-tagged Gbeta and Ggamma
subunits exhibit drastically reduced steady state levels and are absent
from the plasma membrane in phlp1_ cells. Triton X-114 partitioning
suggests that lipid attachment to GFP-Ggamma occurs in wild-type, but not
in phlp1_ and gbeta _ cells. Moreover, Gbeta-gamma dimers could not be
detected in vitro in co-immunoprecipitation assays with phlp1- cell
lysates. Accordingly, in vivo diffusion measurements using fluorescence
correlation spectroscopy showed that while GFP-Ggamma proteins are present
in a complex in wild type cells they are free in phlp1- and gbeta- cells.
Collectively, our data strongly suggest the absence of Gbeta-gamma dimer
formation in Dictyostelium cells lacking PhLP1. We propose that PhLP1
serves as a co-chaperone assisting the assembly of Gbeta and Ggamma into a
functional Gbeta-gamma complex. Thus, phosducin family proteins may fulfil
hitherto unsuspected biosynthetic functions.
Submitted by: Peter Van Haastert [p.j.m.van.haastert@rug.nl]
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Functional analysis of a novel gene, DD3-3, from Dictyostelium discoideum
N. Sakuragi, N. Ogasawara, E. Tanesaka, and M. Yoshida,
Graduate School of Biological Sciences, Nara Institute of Science and
Technology, Ikoma, Nara 630-0101, Japan
Department of Agriculture, Kinki University, Nakamachi, Nara 631-8505,
Japan
Biochem. Biophys. Res. Commun. in press
A novel gene, DD3-3, from Dictyostelium discoideum has been isolated by an
mRNA differential display between a wild-type strain AX2 and a mutant HG794
which is defective in O-glycosylation. Functional analysis of the novel
gene, DD3-3, was conducted by preparing a knockout mutant, DD3-3KO, and a
GST:DD3-3 fusion protein. The mutant DD3-3KO cells were allowed to develop
about 1.5 hours earlier than the wild-type strain AX2 cells. Northern
analysis of the knockout mutant cells showed a remarkable downregulation
of Reg A, cAMP-dependent phosphodiesterase, and overexpression of protein
tyrosine kinase (PTK) during early development and its shutdown during late
development. The relationship between O-glycosylation and phosphorylation
involving Reg A gene is discussed.
Submitted by: Motonobu.Yoshida [yoshida_m@nara.kindai.ac.jp]
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[End Dicty News, volume 24, number 16] 
