dictyNews Electronic Edition Volume 27, number 16 December 1, 2006 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 ========= A 40.7 kDa Rpp30/Rpp1 homologue is a protein subunit of Dictyostelium discoideum RNase P holoenzyme Anastassios Vourekas1, Dimitra Kalavrizioti1, Ioannis K. Zarkadis2, Georgios A. Spyroulias3, Constantinos Stathopoulos4 and Denis Drainas1 Departments of Biochemistry1 and Biology2, School of Medicine, University of Patras, Patras 265 04, Greece. Department of Pharmacy3, University of Patras, Patras 265 04, Greece Department of Biochemistry and Biotechnology4, University of Thessaly, Larissa 412 21, Greece Biochimie, in press RNase P is an essential and ubiquitous endonuclease that mediates the maturation of the 5' ends of all precursor tRNA molecules. The holoenzyme from Dictyostelium discoideum possesses RNA and protein subunits essential for activity, but the exact composition of the ribonucleoprotein complex is still under investigation. Bioinformatic analysis of D. discoideum genome identified seven open reading frames encoding candidate RNase P protein subunits. The gene named drpp30, encodes a protein with a predicted molecular mass of 40.7 kDa that clusters with Rpp1 and Rpp30 RNase P protein subunits from Saccharomyces cerevisiae and human respectively, which have significantly lower molecular masses. Cloning and heterologous expression of DRpp30 followed by immunochemical analysis of RNase P active fractions demonstrates its association with RNase P holoenzyme. Furthermore, we show that DRpp30 can bind D. discoideum RNase P RNA and tRNA transcripts in vitro, giving a first insight of its possible role in D. discoideum RNase P function. Homology modelling using as a template the archaeal Ph1887p, and molecular dynamics simulations of the modeled structure suggest that DRpp30 adopts a TIM-barrel fold. Submitted by Denis Drainas [Drainas@med.upatras.gr] -------------------------------------------------------------------------------- Filamin regulated F-actin assembly is essential for morphogenesis and controls phototaxis in Dictyostelium Nandkumar Khaire, Rolf Mueller, Rosemarie Blau-Wasser, Ludwig Eichinger, Michael Schleicher, Matthias Rief, Tad A. Holak, Angelika A. Noegel Journal of Biological Chemistry, in press Dictyostelium strains lacking the F-actin crosslinking protein filamin (ddFLN) have a severe phototaxis defect at the multicellular slug stage. Filamins are rod-shaped homodimers that cross-link the actin cytoskeleton into highly viscous, orthogonal networks. Each monomer chain of filamin is comprised of an F-actin-binding domain and a rod domain. In rescue experiments only intact filamin re-established correct phototaxis in filamin minus mutants whereas C-terminally truncated filamin proteins that had lost the dimerisation domain and molecules lacking internal repeats but retaining the dimerisation domain did not rescue the phototaxis defect. Deletion of individual rod repeats also changed their subcellular localisation and mutant filamins in general were less enriched at the cell cortex as compared to the full length protein and were increasingly present in the cytoplasm. For correct phototaxis ddFLN is only required at the tip of the slug as expression under control of the cell type specific ecmA promoter and mixing experiments with wild type cells supported phototactic orientation. Likewise, in chimeric slugs wild type cells were primarily found at the tip of the slug which acts as an organiser in Dictyostelium morphogenesis. Submitted by: Angelika A. Noegel [noegel@uni-koeln.de] -------------------------------------------------------------------------------- Induced symbiosis: Distinctive Escherichia coli-Dictyostelium discoideum transferable co-cultures on agar Masahiko Todoriki1, Itaru Urabe1 1Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan Email. riki3@bio.eng.osaka-u.ac.jp Symbiosis, in press Despite the near ubiquity of symbiosis, only a few new symbiotic associations have been reported. The establishment of the unique amoeba-bacterial symbiosis observed by Jeon and his colleagues has been difficult to retrace experimentally mainly because of the failure to grow both partners in pure culture. The details of symbiosis origin and especially laboratory induction are unknown in all cases. Here, we present an experiment in which specific strains of four-year subculture Escherichia coli and Dictyostelium discoideum evolved interdependently to produce a new morphological entity on agar plates. The cocultured organisms lost their pure culture identities under the conditions in which both control organisms retained their independent culturability. Between days 32 and 101 of culturing of E. coli and between days 259 and 645 in D. discoideum pure culture identity was lost. Yet through the four years both organisms could always be cocultured and stored frozen. We traced the emergence of characteristic changes toward a repeatedly inducible symbiotic relationship in pure cultures of both cocultured organisms. Since both the enteric bacterium and the cellular slime mold are free-living and culturable in pure culture, genetically well-characterized. We provide a useful model for the laboratory study of symbiotic evolution. Submitted by: Masahiko Todoriki [todoriki2004@yahoo.co.jp] ============================================================ [End dictyNews, volume 27, number 16]