CSM News
Electronic Edition
Volume 7, number 1
July 6, 1996
Please submit abstracts of your papers as soon as they have been
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Abstracts
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Temporal Regulation of the DICTYOSTELIUM Glycogen Phosphorylase 2 Gene
Charles L. Rutherford*, Ornella Selmin, and Sandra Peters-Weigel
Biology Department, Molecular and Cellular Biology Section, Virginia
Polytechnic Institute and State University, Blacksburg, VA 24061,
Biochem. Biophys. Acta, in press.
The product of the glycogen phosphorylase-2 gene in Dictyostelium
functions to provide the glucose units that are used to construct the
structural components of the terminal stage of development. The
nucleotide sequence of a genomic clone that extended from an Eco R1
site at -1,216 nucleotides from the translational start AUG codon
(-930 nucleotides from the transcriptional start site) to a Rsa I site
at +17 nucleotides is shown. We linked a 1,233 bp upstream gp2
fragment to a luciferase reporter gene in order to study the sequences
that are involved in the temporal expression of the gene. Various
deletions of the promoter-luciferase fusion were then transformed into
Dictyostelium cells. All deletion constructs, from -1,216 to -486
nucleotides from the translational start codon, showed the same
temporal pattern of expression as the authentic gp2 gene, as well as
similar luciferase activities. Removal of an additional 37
nucleotides resulted in nearly 100 fold decrease in activity, yet
retained the normal temporal expression of luciferase. In order to
test if the fragment containing the "C and TAG" boxes was dependent on
its position within the promoter, we amplified this segment and
ligated it to an inactive construct. This fragment, extending from
-461 to -282 bp and containing both TAG and C boxes, was fused to an
inactive construct . This placed the TAG and C boxes 110 bp closer to
the start site of translation than they were in the unmodified
promoter, as well as deleted the segment from -282 to -172. This
resulted in activation of the construct to a luciferase activity that
corresponded to the active promoter, and enabled it to show temporal
expression identical to the full length promoter. Analysis of DNA
binding proteins with the gel shift assay revealed a stage dependent
pattern of proteins that bound to the gp2 promoter. A similar pattern
of temporal expression of the binding proteins was observed with
either the full-length probe or with oligonucleotide probes that
contained sequences that were identified as putative regulatory sites.
Likewise, the full length and oligonucleotide probes demonstrated
identical binding patterns during several steps of purification of the
DNA binding proteins. SDS-PAGE and southwestern blot analysis of a
DNA-affinity purified fraction, identified a 23kD peptide as the
binding protein.
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F. Rivero1, R. Furukawa2, A. A. Noegel1, and M. Fechheimer2# 1.
Max-Planck-Institute for Biochemistry, 82152 Martinsried, FRG 2.
Department of Cellular Biology, University of Georgia, Athens, Georgia
Dictyostelium discoideum Cells Lacking the 34,000 Dalton Actin Binding
Protein Can Grow, Locomote, and Develop, but Exhibit Defects in
Regulation of Cell Structure and Movement: A Case of Partial
Redundancy
J. Cell Biol., in press.
Abstract
Cells lacking the Dictyostelium 34,000 dalton actin bundling
protein, a calcium regulated actin cross-linking protein, were created
in order to probe the function of this polypeptide in living cells.
Cells lacking the 34 kD protein were obtained in strains derived from
AX2 and AX3. Growth, pinocytosis, morphogenesis, and expression of
developmentally regulated genes is normal in cells lacking the 34 kD
protein. In chemotaxis studies, 34 kD- cells were able to locomote
and orient normally, but showed an increased persistence of motility.
The 34 kD- cells also lost bits of cytoplasm during locomotion. The
34 kD- cells exhibited either an excessive number of long and branched
filopodia, or a decrease in filopodial length and an increase in the
total number of filopodia per cell depending on the strain.
Re-expression of the 34 kD protein in the AX2 derived strain led to a
"rescue" of the defect in persistence of motility, and of the excess
numbers of long branched filopodia, demonstrating that these defects
are due to the absence of the 34 kD protein. We explain the results
through a model of partial functional redundancy. Numerous other
actin cross-linking proteins in Dictyostelium may be able to
substitute for some functions of the 34 kD protein in the 34 kD-
cells. The observed phenotype is presumed due to functions that
cannot be adequately supplanted by a substitution of another actin
cross-linking protein. We conclude that the 34 kD actin bundling
protein is not essential for growth, but plays an important role in
dynamic control of cell shape and cytoplasmic structure.
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[End CSM-News, volume 7, number 7]