dictyNews Electronic Edition Volume 36, number 17 June 24, 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 ========= Self-recognition in social amoebae is mediated by allelic pairs of tiger genes Shigenori Hirose*, Rocio Benabentos*, Hsing-I Ho, Adam Kuspa# and Gad Shaulsky# Baylor College of Medicine, Houston, TX * equal contribution; # corresponding authors Science, in press Abstract: Free-living cells of the social amoebae Dictyostelium discoideum can aggregate and develop into multicellular fruiting bodies in which many altruistically die as they become stalk cells that support the surviving spores. Dictyostelium cells exhibit kin-discrimination Š a potential defense against cheaters, which sporulate without contributing to the stalk. Kin-discrimination depends on strain relatedness and the polymorphic genes tgrB1 and tgrC1 are potential components of that mechanism. Here we demonstrate a direct role for these genes in kin-discrimination. We show that a matching pair of tgrB1 and tgrC1 alleles is necessary and sufficient for attractive self-recognition, which is mediated by differential cell-cell adhesion. We propose that TgrB1 and TgrC1 proteins mediate this adhesion through direct binding. This system is a genetically-tractable ancient model of eukaryotic self-recognition. Submitted by Gad Shaulsky [gadi@bcm.edu] -------------------------------------------------------------------------------- Identification of Calmodulin and MlcC as Light Chains for Dictyostelium Myosin-I Isozymes Scott W. Crawley , Janine Liburd , Kristopher Shaw, Yoojin Jung, Steven P. Smith and Graham P. C™tˇ From the Department of Biochemistry, QueenÕs University, Kingston, Ontario, Canada K7L 3N6  These authors contributed equally to this work Biochemistry, in press Dictyostelium discoideum express seven single-headed myosin-I isozymes (MyoA-MyoE and MyoK) that drive motile processes at the cell membrane. The light chains for MyoA and MyoE were identified by expressing Flag-tagged constructs consisting of the motor domain and the two IQ motifs in the neck region in Dictyostelium. The MyoA and MyoE constructs both co-purified with calmodulin. Isothermal titration calorimetry (ITC) showed that apo-calmodulin bound to peptides corresponding to the MyoA and MyoE IQ motifs with micromolar affinity. In the presence of calcium, calmodulin cross-linked two IQ motif peptides, with one domain binding with nanomolar affinity and the other with micromolar affinity. The IQ motifs were required for the actin-activated MgATPase activity of MyoA but not MyoE; however, neither myosin exhibited calcium-dependent activity. A Flag-tagged construct consisting of the MyoC motor domain and the three IQ motifs in the adjacent neck region bound a novel 8.6 kDa two EF-hand protein named MlcC, for myosin light chain for MyoC. MlcC is most similar to the C-terminal domain of calmodulin but does not bind calcium. ITC studies showed that MlcC binds IQ1 and IQ2 but not IQ3 of MyoC. IQ3 contains a proline residue that may render it non-functional. Each long-tailed Dictyostelium myosin-I has now been shown to have a unique light chain (MyoB- MlcB, MyoC-MlcC and MyoD-MlcD), whereas the short-tailed myosins-I, MyoA and MyoE, have the multi-functional calmodulin as a light chain. The diversity in light chain composition is likely to contribute to the distinct cellular functions of each myosin-I isozyme. Submitted by Scott W. Crawley [crawleys@queensu.ca] ============================================================== [End dictyNews, volume 36, number 17]