dictyNews Electronic Edition Volume 36, number 12 April 8, 2011 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. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= Sequence and generation of mature ribosomal RNA transcripts in Dictyostelium discoideum Carsten Boesler1, Janis Kruse1, Fredrik Sšderbom2, and Christian Hammann1 1 Heisenberg Research Group Ribogenetics, Technical University of Darmstadt, 64287 Darmstadt, Germany 2 Department of Molecular Biology, Uppsala Biomedical Center, Swedish University of Agricultural Sciences, S-75124 Uppsala, Sweden JBC, in press The amoeba Dictyostelium discoideum is a well-established model organism for studying numerous aspects of cellular and developmental functions. Its ribosomal RNA (rRNA) is encoded in an extrachromosomal palindrome that exists in ca. 100 copies in the cell. In this study, we have set out investigate the sequence of the expressed rRNA. For this, we have ligated the rRNA ends and performed RT-PCR on these circular RNAs. Sequencing revealed that the mature 26S, 17S, 5.8S and 5S rRNAs have sizes of 3741, 1871, 162 and 112 nucleotides, respectively. Unlike published, all mature rRNAs of a type uniformly display the same start and end nucleotides in the analyzed AX2 strain. We show the existence of a short-lived primary transcript covering the rRNA transcription unit of 17S, 5.8S and 26S rRNA. Northern blots and RT-PCR reveal that from this primary transcript two precursor molecules of the 17S and two precursors of the 26S rRNA are generated. We have also determined the sequences of these precursor molecules, and based on this data, we propose a model for the maturation of the rRNAs in Dictyostelium discoideum that we compare to the processing of the rRNA transcription unit of Saccharomyces cerevisiae. Submitted by Christian Hammann [hammann@bio.tu-darmstadt.de] -------------------------------------------------------------------------------- Genetically tagged TRE5-A retrotransposons reveal high amplification rates and authentic target site preference in the Dictyostelium discoideum genome Oliver Siol, Thomas Spaller, Jana Schiefner and Thomas Winckler School of Biology and Pharmacy, Institute of Pharmacy, Department of Pharmaceutical Biology, University of Jena, Semmelweisstrasse 10, 07743 Jena, Germany Nucleic Acids Research, in press Retrotransposons contribute significantly to the evolution of eukaryotic genomes. They replicate by producing DNA copies of their own RNA, which are integrated at new locations in the host cell genome. In the gene-dense genome of the social amoeba Dictyostelium discoideum, retrotransposon TRE5-A avoids insertional mutagenesis by targeting the transcription factor (TF) IIIC/IIIB complex and integrating ~50 bp upstream of tRNA genes. We generated synthetic TRE5-A retrotransposons (TRE5-Absr) that were tagged with a selection marker that conferred resistance to blasticidin after a complete retrotransposition cycle. We found that the TRE5-Absr elements were efficiently mobilized in trans by proteins expressed from the endogenous TRE5-A population found in D. discoideum cells. ORF1 protein translated from TRE5-Absr elements significantly enhanced retrotransposition. We observed that the 5' untranslated region of TRE5-A could be replaced by an unrelated promoter, whereas the 3' untranslated region of TRE5-A was essential for retrotransposition. A predicted secondary structure in the RNA of the 3' untranslated region of TRE5-A may be involved in the retrotransposition process. The TRE5-Absr elements were capable of identifying authentic integration targets in vivo, including formerly unnoticed, putative binding sites for TFIIIC on the extrachromosomal DNA element that carries the ribosomal RNA genes. Submitted by Thomas Winckler [t.winckler@uni-jena.de] -------------------------------------------------------------------------------- The Role of Extracellular Cations in Cell Motility, Polarity and Chemotaxis David R. Soll, Deborah Wessels, Daniel F. Lusche, Spencer Kuhl, Amanda Scherer, and Shawna Grimm Research and Reports in Biology http://www.dovepress.com/articles.php?article_id=7033 The concentrations of cations in the aqueous environment of free living organisms and cells within the human body influence motility, shape and chemotaxis. The role of extracellular cations is usually perceived to be the source for intracellular cations in the process of homeostasis. The role of surface molecules that interact with extracellular cations is believed to be that of channels, transporters and exchangers. However, the role of Ca++ as a signal and chemoattractant, and the discovery of the Ca++ receptor CaR, have demonstrated that extracellular cations can function as signals at the cell surface, and the plasma membrane molecules they interact with can function as bona fide receptors that activate coupled signal transduction pathways, associated molecules in the plasma membrane or the cytoskeleton. With this perspective in mind, we have reviewed the cationic composition of aqueous environments of free living cells and cells that move in multicellular organisms, most notably humans, the range of molecules interacting with cations at the cell surface, the concept of a cell surface cation receptor, and the roles extracellular cations and the plasma membrane proteins that interact with them play in the regulation of motility, shape and chemotaxis. Hopefully, the perspective of this review will increase awareness of the roles extracellular cations play and the possibility that many of the plasma membrane proteins that interact with them could also play roles as receptors. Submitted by Wessels Deborah [deborah-wessels@uiowa.edu] ============================================================== [End dictyNews, volume 36, number 12]