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]