CSM News Electronic Edition Volume 6, number 17 June 29, 1996 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to CSM-News@worms.cmb.nwu.edu. Back issues of CSM-News, the CSM Reference database and other useful information is available by anonymous ftp from worms.cmb.nwu.edu [165.124.233.50], via Gopher at the same address, or by World Wide Web at the URL "http://worms.cmb.nwu.edu/dicty.html" =========== Abstracts =========== CONSTITUTIVELY ACTIVE ADENYLYL CYCLASE MUTANT REQUIRES NEITHER G PROTEINS NOR CYTOSOLIC REGULATORS Carole A. Parent and Peter N. Devreotes Department of Biological Chemistry, Johns Hopkins School of Medicine, Baltimore, MD J. Biol. Chem., in press. Receptor-mediated G protein linked adenylyl cyclase systems are universal signal transducers. We exploited the essential role of this cascade in Dictyostelium development to screen for random mutations in the catalytic component, ACA. This enzyme is activated by G protein beta/gamma-subunits acting in concert with a novel cytosolic regulator, CRAC. By suppression of the CRAC-null phenotype, we isolated constitutively active versions to the enzyme that require neither exogenous stimuli nor internal regulators. One mutant displayed a fifteen-fold increase in its Vmax. It harbors a single amino acid substitution (L394S) affecting a conserved residue located in the first cytoplasmic loop near the N-terminal hydrophobic domain of ACA. The screening procedure can be adapted for isolation of constitutive mutations in mammalian adenylyl cyclases. -------------------------------------------------------------------- Dictyostelium discoideum cobB mutants have reduced heavy metal accumulation associated with gene amplification J.E.Hughes, K.L.DeLange and D.L.Welker. Mol. Gen. Genet., in press. ABSTRACT Wild type Dictyostelium discoideum cells growing on non-toxic levels of nickel chloride or cobaltous chloride accumulate 2-3.5X as much nickel and at least 1.5X as much cobalt as cobB mutants. The cobB trait is dominant, confers unstable cobalt and nickel resistance and is correlated with up to 50 copies of a linear extrachromosomal DNA, approximately 100 kilobases in length, derived from linkage group III. Independent cobB mutants can be obtained by selection on medium containing either cobalt or nickel. The amplified DNA can be transferred to wild type strains by electroporation. Strains with mutations at the independent cobalt resistance locus, cobA, accumulate the same amount of cobalt, but more nickel than wild type strains. Our results are consistent with the cobA mutant phenotype being due to internal sequestration of cobalt, and the cobB mutant phenotype being due to reduced net uptake of cobalt and nickel. Energy dependent nickel export was detectable in wild type and cobB mutant strains but its role in heavy metal resistance has not yet been proved. --------------------------------------------------------------------- [End CSM News, volume 6, number 17]