dictyNews Volume 29 Number 10

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dictyNews 
Electronic Edition 
Volume 29, number 10 
October 5, 2007 

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. 

 
========= 
Abstracts 
========= 

 

Protein interactions involved in tRNA gene-specific integration of  
Dictyostelium non-long terminal repeat retrotransposon TRE5-A 

Thanh Chung(1), Oliver Siol(2), Theodor Dingermann(1,3) and  
Thomas Winckler(2) 

(1) Institut fuer Pharmazeutische Biologie, Universitaet Frankfurt/M.  
(Germany) 
(2) Lehrstuhl fuer Pharmazeutische Biologie, Universitaet Jena (Germany) 
(3) Zentrum für Arzneimittelforschung, Entwicklung und Sicherheit,  
Frankfurt (Germany) 

 
Mol. Cell. Biol., in press 

Mobile genetic elements that reside in gene-dense genomes face the problem  
of avoiding devastating insertional mutagenesis of genes in their host cell  
genomes. To meet this challenge, some yeast long terminal repeat (LTR)  
retrotransposons have evolved targeted integration at safe sites in  
immediate vicinity of tRNA genes. Integration of yeast Ty3 is mediated  
by interactions of retrotransposon protein with the tRNA gene-specific  
transcription factor TFIIIB.  In the genome of the social amoeba  
Dictyostelium discoideum the non-LTR retrotransposon TRE5-A integrates  
~48 bp upstream of tRNA genes, yet little is known about how the  
retrotransposon identifies integration sites. Here, we show direct  
protein interactions of TRE5-A ORF1 protein with subunits of TFIIIB,  
suggesting that ORF1p is a component of the TRE5-A pre-integration  
complex that determines integration sites. Our results demonstrate that  
evolution has put forth similar solutions to prevent damage of diverse,  
compact genomes by different classes of mobile elements. 

 
Submitted by: Thomas Winckler [t.winckler@uni-jena.de] 
-------------------------------------------------------------------------------- 

 
The Ste20-like kinase SvkA of Dictyostelium discoideum is essential for  
late stages of cytokinesis 

Meino Rohlfs, Rajesh Arasada, Petros Batsios, Julia Janzen and  
Michael Schleicher 

Adolf-Butenandt-Institut/Zellbiologie, Ludwig-Maximilians-Universitaet, 
Schillerstr. 42, 80336 Muenchen, Germany. 

 
JCS, in press 

The genome of the social amoeba Dictyostelium discoideum codes for about  
285 kinases which represents 2.6% of the total genome and suggests a  
similar signaling complexity as in yeast and humans. The behavior of  
D. discoideum as amoeba and during development relies heavily on the  
fast rearrangements of the actin cytoskeleton. Here we describe the  
knockout phenotype of the severin kinase gene (svkA), a homolog of the  
MST3, MST4 and YSK1 kinases in humans. SvkA-minus cells show drastic  
defects in cytokinesis, development and directed slug movement. The  
cytokinesis defect is most prominent leading to multinucleated cells  
sometimes with more than 30 nuclei. The defect arises from the frequent  
disability of svkA-minus cells to keep the symmetry during cleavage  
furrow formation and to sever the last cytosolic connection. We  
demonstrate that GFP-SvkA is enriched at the centrosome and localizes  
to the midzone during the final stage of cell division. This distribution  
is mediated by the C-terminal half of the kinase, whereas a rescue of  
the phenotypic changes requires the active N-terminal kinase domain as  
well. The data suggest that SvkA is part of a regulatory pathway from the  
centrosome to the midzone, thus regulating completion of cell division.  

 
Submitted by: Meino Rohlfs [Meino.Rohlfs@lmu.de] 
-------------------------------------------------------------------------------- 

 
Regulation of Rap1 Activity by RapGAP1 Controls Cell Adhesion at the  
Front of Chemotaxing Cells 

Taeck J. Jeon, Dai-Jen Lee, Susan Lee, Gerald Weeks, and Richard A. Firtel 

 
Journal of Cell Biology, in press 

Spatial and temporal regulation of Rap1 is required for proper myosin  
assembly and cell adhesion during cell migration in Dictyostelium. Here,  
we identify a Rap1 GAP (RapGAP1) that helps mediate cell adhesion by  
negatively regulating Rap1 at the leading edge. Defects in spatial  
regulation of the cell attachment at the leading edge in rapGAP1- (null)  
cells or cells overexpressing RapGAP1 (RapGAP1OE) leads to defective  
chemotaxis. rapGAP1- cells have extended chemoattractant-mediated Rap1  
activation kinetics and decreased MyoII assembly, whereas RapGAP1OE  
cells show reciprocal phenotypes. We see that RapGAP1 translocates to  
the cell cortex in response to chemoattractant stimulation and localizes  
to the leading edge of chemotaxing cells via an F-actin-dependent pathway.  
RapGAP1 localization is negatively regulated by cortexillin (Ctx), an F-actin  
bundling protein that functions during cytokinesis. Loss of Ctx leads to  
constitutive and uniform RapGAP1 cortical localization. We suggest that  
RapGAP1 functions in the spatial and temporal regulation of attachment  
sites through MyoII assembly via regulation of Rap1-GTP. 

 
Submitted by: Rick Firtel [rafirtel@ucsd.edu] 
============================================================== 
[End dictyNews, volume 29, number 10]