dictyNews Electronic Edition Volume 30, number 12 April 11, 2008 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 ========= Linking Ras to myosin function: RasGEF Q, a Dictyostelium exchange factor for RasB, affects myosin II functions Subhanjan Mondal, Deenadayalan Bakthavatsalam, Paul Steimle, Berthold Gassen, Francisco Rivero, Angelika A. Noegel Accepted, J. Cell Biol. RasGEF Q, a nucleotide exchange factor from Dictyostelium, is a 143 kDa protein containing RasGEF domains and a DEP domain. Here, we show that RasGEF Q can bind to F-actin, has the potential to form complexes with MHCK A that contain active RasB, and is the predominant exchange factor for RasB. Overexpression of the RasGEF Q GEF domain activates RasB, causes enhanced recruitment of MHCK A to the cortex, and leads to cytokinesis defects in suspension, phenocopying cells expressing constitutively active RasB and myosin null mutants. RasGEF Q− mutants have defects in cell sorting and slug migration during later stages of development, in addition to cell polarity defects. Further, RasGEF Q− mutants have increased levels of unphosphorylated myosin II, resulting in myosin II overassembly. Together our results suggest that starvation signals through RasGEF Q to activate RasB, which then regulates processes requiring myosin II. Submitted by: Angelika Noegel [noegel@uni-koeln.de] -------------------------------------------------------------------------------- Mitochondrial Genome Evolution in the Social Amoebae Andrew J. Heidel, Gernot Glöckner Genome Analysis Group Leibniz Institute for Age Research Fritz Lipmann Institute 07745 Jena, Germany MBE, in press Most mitochondria contain a core set of genes required for mitochondrial function, but beyond this base there are variable genomic features. The mitochondrial genome of the model species Dictyostelium discoideum demonstrated that the social amoebae mitochondria genomes have a size between those of metazoans and plants, but no comparative study of social amoebae has been performed. Here, we present a comparative analysis of social amoebae mitochondrial genomes using D. discoideum, D. citrinum, D. fasciculatum and Polysphondylium pallidum. The social amoebae mitochondria have similar sizes, AT content, gene content and have a high level of synteny except for one segmental rearrangement and extensive displacement of tRNAs. From the species that contain the rearrangement, it can be concluded that the event occurred late in the evolution of social amoebas. A phylogeny using 36 mitochondrial genes produced a well-supported tree suggesting that the pairs of D. discoideum/D. citrinum and D. fasciculatum/P. pallidum are sister species although the position of the root is not certain. Group I introns and endonucleases are variable in number and location in the social amoebae. Phylogenies of the introns and endonucleases suggest that there have been multiple duplications or extinctions and that endonucleases have the ability to insert into new areas. An analysis of dN/dS ratios in mitochondrial genes revealed that among groups of genes, ATP synthase complex genes change more rapidly while cytochrome oxidase and NADH dehydrogenase genes had the slowest rate. The genetic codes of D. citrinum, P. pallidum and D. fasciculatum are the universal code although D. fasciculatum does not use the TGA stop codon. In D. fasciculatum, we demonstrate for the first time that a mitochondrial genome without the TGA stop codon still uses the release factor RF2 that recognizes TGA. Theories of how the genetic code can change and why RF2 may be a constraint against switching codes are discussed. Submitted by: Gernot Gloeckner [gernot@fli-leibniz.de] ============================================================== [End dictyNews, volume 30, number 12]