CSM News Electronic Edition Volume 5, number 17 December 16, 1995 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to CSM-News@worms.cmsbio.nwu.edu. Back issues of CSM-News, the CSM Reference database and other useful information is available by anonymous ftp from worms.cmsbio.nwu.edu [165.124.233.50], via Gopher at the same address, or by World Wide Web at the URL "http://worms.cmsbio.nwu.edu/dicty.html" ======================= Happy Holidays To All ======================= =========== Abstracts =========== Gottwald, U., Brokamp, R., Karakesisoglou, I., Schleicher, M., Noegel, A. A. Identification of a cyclase associated protein (CAP) homologue in D. discoideum and characterization of its interaction with actin Mol. Biol. Cell, in press Abstract In a search for novel actin binding proteins in Dictyostelium discoideum we have isolated a cDNA clone coding for a protein of approximately 50 kDa which is highly homologous to the class of adenylyl cyclase associated proteins (CAP). In Saccharomyces cervisiae the amino-terminal part of CAP is involved in the regulation of the adenylyl cyclase whereas the loss of the carboxyl-terminal domain results in morphological and nutritional defects. To study the interaction of Dictyostelium CAP with actin the complete protein and its aminoterminal and carboxyterminal domains were expressed in E. coli and used in actin binding assays. CAP sequestered actin in a Ca2+ independent way. This activity was localized to the carboxyl-terminal domain. Cap and its carboxyl-terminal domain led to a fluorescence enhancement of pyrene-labelled G-actin up to 50% indicating a direct interaction, whereas the amino-terminal domain did not enhance. In polymerization as well as in viscometric assays the ability of the carboxyl- terminal domain to sequester actin and to prevent F-actin formation was approx. 2 times higher than that of intact CAP. The sequestering activity of full length CAP could be inhibited by phosphatidylinositol 4,5- bisphosphate (PIP2), whereas the activity of the carboxyl-terminal domain alone was not influenced suggesting that the aminoterminal half of the protein is required for the PIP2 modulation of the CAP function. In profilin-minus cells the CAP concentration is increased by approximately 73%, indicating that CAP was enriched at anterior and posterior plasma membrane regions. Only a weak staining of the cytoplasm was observed. In chemotactically stimulated cells the protein was very prominent in leading fronts. The data suggest an involvement of D. discoideum CAP in microfilament reorganization near the plasma membrane in a PIP2 regulated manner. -------------------------------------------------------------------- Some Repair-Deficient Mutants of Dictyostelium discoideum Display Enhanced Susceptibility to Bleomycin. Reginald A. Deering, Robert B. Guyer, Lenore Stevens, and Theresa E. Watson-Thais Antimicrobial Agents and Chemotherapy, in press, Abstract Dictyostelium discoideum is very resistant to DNA-damaging agents. Bleomycin is a DNA-damaging cancer chemotherapeutic agent produced in soil by Streptomyces verticellus . Mutants of D. discoideum isolated in this laboratory are more sensitive than the wild type to a variety of DNA-damaging agents, including certain chemicals, ultraviolet light, and gamma rays. Here we extend these studies to compare the sensitivities of these strains to bleomycin. The growth rate of the very sensitive mutant rad B was reduced to 10% by 20 times less bleomycin than the parental repair proficient rad + strain. The rad + and rad C cells sustained 90% lethality at 54 mU bleomycin/ml, while 90% of rad A and rad D cells were killed by 0.5 mU/ml. The rad B cells were the most sensitive, showing 90% lethality at 0.3 mU bleomycin/ml. These results indicate that the levels of cross-resistance of D. discoideum wild-type and mutant cells, seen previously for radiation and other chemicals, extends to bleomycin, a toxic agent likely to be present in their natural environment. Hence, their highly efficient DNA repair capabilities may result in evolution from the necessity of coping with DNA-damaging chemicals produced by other microorganisms in soil. ------------------------------------------------------------------- PROTEASE-SENSITIVE COMPONENT(S) ON THE CELL SURFACE PREVENTS SELF-FUSION IN A BISEXUAL STRAIN OF Dictyostelium discoideum Hideko Urushihara and Kazuhiro Aiba University of Tsukuba, Institute of Biological Sciences, Tsukuba, Ibaraki 305 Japan TEL: 0298-53-4910, FAX: 0298-53-6614 e-mail: d402hu@sakura.cc.tsukuba.ac.jp Cell Structure and Function, in press ABSTRACT The sexual cycle of the cellular slime mold Dictyostelium discoideum offers a suitable system to analyze the mechanism of cell recognition during mating. Sexual cell fusion in D. discoideum typically occurs between complementary heterothallic strains. In addition, several bisexual strains are known which undergo sexual cell fusion with heterothallic strains of either mating type, but cannot do so by them- selves. In the present study, trypsin digestion of cell surface molecules was found to induce self-fusion in a bisexual strain WS2162, suggesting the presence on the cell surface of a self-recognition molecule whose homophilic interaction interferes with the cell fusion mechanism. ----------------------------------------------------------------------- [End CSM-News, volume 5, number 17]