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Mol. Cell. Biol., 05 1996, 2431-2444, Vol 16, No. 5
M Gamper, PK Howard, T Hunter and RA Firtel
PTP3, the third nonreceptor protein tyrosine phosphatase identified in
Dictyostelium discoideum, has a single catalytic protein tyrosine
phosphatase domain. Recombinant PTP3 exhibited phosphatase activity that
was inhibited by vanadate. PTP3 is expressed at a moderate level during
growth. The level of transcripts increased between growth and 8 h of
development and declined thereafter. Expression of lacZ under the control
of the PTP3 promoter indicated a spatial localization of PTP3 in the
anterior-like and prestalk cell types. There are two copies of the PTP3
gene in this haploid organism. Disruption of one copy led to a slow-growth
phenotype. We were unable to obtain a strain with disruptions in both PTP3
genes. Overexpression of wild-type PTP3 led to slower growth rates and the
formation of large aggregation streams. These streams split into smaller
aggregates, many of which then arrested in development. Overexpression of a
catalytically inactive mutation (Cys to Ser) had no effect on growth rate;
however, this strain also formed large aggregation streams that later split
up into large and small mound structures and became fruiting bodies of
various sizes. Antiphosphotyrosine Western blot (immunoblot) analysis of
total cell proteins showed that the pattern of protein tyrosine
phosphorylation was specifically altered in PTP3 mutants. Addition of
growth medium to starving cells and a subsequent replacement with
nonnutrient buffer led to reciprocal changes in the pattern of several
phosphotyrosine proteins, including a protein of approximately 130 kDa.
Analysis of strains overexpressing active or inactive PTP3 suggested that
p130 is a potential substrate of PTP3. A transient posttranslational
phosphorylation of PTP3 further supported the role of PTP3 in these
processes. The data obtained strongly suggest new regulatory functions for
PTP3 that are distinct from those described earlier for D. discoideum PTP1
and PTP2.
Copyright © 1996, American Society for Microbiology
Multiple roles of the novel protein tyrosine phosphatase PTP3 during Dictyostelium growth and development
Department of Biology, Center for Molecular Genetics, University of California, San Diego, 92093-0634, USA.
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