CSM News
Electronic Edition
Volume 6, number 13
May 25, 1996

Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to CSM-News@worms.cmb.nwu.edu.

Back issues of CSM-News, the CSM Reference database and other useful
information is available by anonymous ftp from worms.cmb.nwu.edu
[165.124.233.50], via Gopher at the same address, or by World Wide Web
at the URL "http://worms.cmb.nwu.edu/dicty.html"

===========
 Abstracts
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RNGB: a Dictyostelium RING finger protein that is specifically located
in maturing spore cells

Takefumi Kawata,1 Jane B. Steel2 and Jeffrey G. Williams1

1. MRC Laboratory of Molecular Cell Biology and Department of Biology,
University College London Gower St, London WC1E 6BT 2. Imperial Cancer
Research Fund, 44 Lincoln's Inn Fields, London WC2A 3PX, UK

FEBS Letts., in press.

Abstract

   The RING finger is a form of zinc finger motif found in proteins of
widely varying biological function.  The Dictyostelium RNGB protein
contains a RING finger and also a K box, a sequence motif found in
several plant homeotic proteins. The rngB mRNA is present at low
concentration in growing cells and gradually increases in abundance
throughout development.  However, the RNGB protein is not detected
until culmination and we present evidence that suggests it is
translationally regulated. The protein is specifically localised in
maturing spore cells and is cytoplasmic, suggesting that the RING
finger does not function as a DNA binding domain.

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Acid-activatable Cysteine Proteinases in the Cellular Slime Mold 
Dictyostelium discoideum.  The Journal of Biological Chemistry, accepted.

Michael J. North(1), Kay Nicol(1), Todd W. Sands(2), and David A. Cotter(2)
From (1) Department of Biological and Molecular Sciences, University of 
Stirling, Stirling, FK9 4LA, Scotland and (2)Department of Biological 
Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada. 
Please send correspondence to D. A. Cotter.

J. Biol. Chem., in press.

ABSTRACT

   Studies of the cysteine proteinases of the cellular slime mold
Dictyostelium discoideum have been aided by a simple acid treatment
step that was incorporated into the standard one-dimensional
gelatin-sodium dodecyl sulfate-polyacrylamide gel electrophoresis
assay procedure.  The step involved immersing the separating gel in
10% (v/v) glacial acetic acid for 30-60 s immediately after
electrophoresis.  This modified approach revealed the presence of
acid-activatable forms of some enzymes with noticeable increases in
their ability to hydrolyze gelatin, a substrate present in the sodium
dodecyl sulfate-polyacrylamide gels, and peptidyl
amidomethylcoumarins.  The activation has been analyzed using extracts
of dormant spores from which cysteine proteinase activity had
previously appeared low or virtually absent.  The major
acid-activatable proteinase had an apparent molecular mass of 48 kDa.
Its activation was not due to autocatalysis as it was not prevented by
mercuric chloride, an inhibitor of the enzyme, and was not accompanied
by a significant change in electrophoretic mobility.  It was most
likely due to a conformational change and/or the removal of a low
molecular weight inhibitor.  The acid treatment has also revealed the
presence of acid-activatable cysteine proteinases in vegetative cells,
in which cysteine proteinase activity is present at high levels, as
well as among enzymes from the developmental cells which have much
lower cysteine proteinase activity.  Indeed novel developmental forms
were detected at some stages.  These results provide additional
insight concerning cysteine proteinase expression at various stages
during development in the slime molds.  A developmental model is
presented which suggests that the crypticity of the cysteine
proteinases in dormant spores may be governed by proton pumps and
endogenous lysosomotropic agents.

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[End CSM-News, volume 6, number 13]