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.

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===========
 Abstracts
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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.

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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. 

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[End CSM News, volume 6, number 17]