Dicty News
Electronic Edition
Volume 9, number 6
4 September 1997

Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to CSM-News@nwu.edu.

Back issues of CSM-News, the CSM Reference database and other useful
information is available at the Dictyostelium Web Page 
"http://dicty.cmb.nwu.edu/dicty/dicty.html"

===========
 Abstracts
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Characterization of a novel small RNA encoded by mitochondrial DNA of
Dictyostelium discoideum

Min Pi1, Takahiro Morio1, Hideko Urushihara1 and Yoshimasa Tanaka1,2

1Institute of Biological Sciences and 2Center for TARA*, University of
Tsukuba, Tsukuba, Ibaraki 305, Japan

*Tsukuba Advanced Research Alliance, (TARA researcher for Sakabe project)

Mol. Gen. Genet. In press

Abstract 

   In this study, we analyzed a mitochondrial small (ms) RNA in Dictyostelium
discoideum consisting of 129 nucleotides and which had a GC content of only
22.5%. In the mitochondrial DNA, a single copy gene (msr) for the ms RNA
was located downstream of the gene for large subunit rRNA. The location of
msr was similar to that of the 5S rRNA gene of prokaryotes and
chloroplasts, but clearly different from mitochondria of plants, liverwort
and the chlorophycean alga Prototheca wikerhamii, in which small subunit
rRNA and 5S rRNA genes are closely linked. The primary sequence of ms RNA
showed low homology with mitochondrial 5S rRNA from plants, liverwort and
the chlorophycean alga, but the proposed secondary structure of ms RNA was
similar to that of common 5S rRNA. In addition, ms RNA showed a highly
conserved GAAC sequence in the same loop as in common 5S rRNA. However, ms
RNA was detected mainly in the mitochondrial 25000 x g supernatant fraction
which was devoid of ribosomes. It is possible that ms RNA is a descendant
of mitochondrial 5S rRNA.

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Consequences to Disruption of the Gene Encoding the a-Glucosidase II Used
for N-linked Oligosaccharide Trimming in Dictyostelium discoideum

Hudson H. Freeze#, Marion Lammertz#, Negin Iranfar*, Danny Fuller*,
K. Panneerselvam#, and William F. Loomis*

*Department of Biology, University of California San Diego, La Jolla, CA  92093
#The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, CA  92093

Developmental Genetics, in press.

SUMMARY
   We have identified and disrupted the gene coding for alpha-glucosidase 
II in Dictyostelium discoideum. This enzyme is responsible for removing 
two alpha 1,3-linked glucose residues from N-linked oligosaccharides 
on newly synthesized glycoproteins. Mutagenesis by restriction enzyme 
mediated integration (REMI) generated a clone, DG1033, which grows well 
but forms abnormal fruiting bodies with short,thick stalks. The strain 
has no measurable alpha-glucosidase II activity and makes incompletely 
processed N-linked oligosacccharides that are abnormally large and have 
fewer sulfate and phosphate esters. The morphological, enzymatic, and 
oligosaccharide profile phenotypes of the disruption mutant are all 
recapitulated by a targeted disruption of the normal gene. Furthermore, 
all of these defects are corrected in cells transformed with a normal, 
full length copy of the gene. The phenotypic characteristics of DG1033 
as well as chromosomal mapping of the disrupted gene indicate that it 
is the site of the previously characterized modA mutation. The 
Dictyostelium gene is highly homologous to alpha-glucosidase II genes 
in human, pig, C. elegans and yeast. Although various cell lines have 
been reported to be defective in alpha-glucosidase II activity, 
disruption of the Dictyostelium gene gives the first example of a clear 
developmental phenotype associated with loss of this enzyme.

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[End CSM News, volume 9, number 6]