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dictyNews Volume 25 Number 15
dictyNews
Electronic Edition
Volume 25, number 15
December 16, 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 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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Tamao Saito1,2, Graham W. Taylor3, Ji-ChunYang1, David Neuhaus1, Dmitry
Stetsenko1, Atsushi Kato2 and Robert R. Kay1
Biochimica et Biophysica Acta, in press
Developing Dictyostelium discoideum amoebae form a stalked fruiting body in
which individual cells differentiate into either stalk cells or spores. The
major known inducer of stalk cell differentiation is the chlorinated
polyketide DIF-1 (1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl)hexan-1-one);
however a mutant blocked in the terminal step of DIF-1 biosynthesis still
produces one of the prestalk cell subtypes - the pstA cells – as well as s
ome mature stalk cells. We therefore searched for additional stalk
cell-inducing factors in the medium supporting development of this mutant.
These factors were purified by solvent extraction and HPLC and identified
by mass spectroscopy and NMR. The mutant lacked detectable DIF-2 and DIF-3
(the pentanone and deschloro homologues of DIF-1) but four major stalk
cell-inducing activities were detected, of which three were identified.
Two compounds were predicted intermediates in DIF-1 biosynthesis: the
desmethyl, and desmethyl-monochloro analogues of DIF-1 (dM-DIF-1 and Cl-THPH
respectively), supporting the previously proposed pathway of DIF-1
biosynthesis. The third compound was a novel factor and was identified as
4-methyl-5-pentylbenzene-1,3-diol (MPBD) with the structure confirmed by
chemical synthesis. To investigate the potential roles of these compounds
as signal molecules, their effects on morphological stalk and spore
differentiation were examined in cell culture. All three induced
morphological stalk cell differentiation. We found that synthetic MPBD also
stimulated spore cell differentiation. Now that these factors are known
to be produced and released during development, their biological roles can
be pursued further.
Submitted by: Tamao Saito [tasaito@sci.hokudai.ac.jp]
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Retention and Loss of Amino Acid Biosynthetic Pathways Based on Whole-genome
Sequences
Samuel H. Payne and William F. Loomis
Bioinformatics Program, Division of Biological Sciences
University of California San Diego, La Jolla CA 92093 USA
Eukaryotic Cell, in press
Plants and fungi can synthesize each of the 20 amino acids using biosynthetic
pathways inherited from their bacterial ancestors. However, the ability to
synthesize 9 amino acids (phe, trp, ile, leu, val, lys, his, thr, and met)
was lost in a wide variety of eukaryotes that evolved the ability to feed on
other organisms. Since the biosynthetic pathways and their respective enzymes
are well characterized, orthologs can be recognized in whole genomes to
understand when in evolution pathways were lost. The pattern of pathway loss
and retention was analyzed in the complete genomes of three early diverging
protist parasites, the amoeba Dictyostelium, and six animals. The nine
pathways were lost independently in animals, Dictyostelium, Leishmania,
Plasmodium and Cryptosporidium. Seven additional pathways appear to have
been lost in one or another parasite demonstrating that they are dispensable
in a rich nutritional environment. Our predictions of pathways retained and
pathways lost based on computational analyses of whole genomes are validated
by minimal media studies in mammals, fish, worms and Dictyostelium. The
apparent selective advantages of retaining biosynthetic capabilities for
amino acids available in the diet are considered.
Submitted by: Bill Loomis [wloomis@ucsd.edu]
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[End dictyNews, volume 25, number 15] 
