Evidence for protein-tyrosine-phosphatase catalysis proceeding via a cysteine-phosphate intermediate.

A recombinant protein-tyrosine-phosphatase has been expressed in Escherichia coli and purified to a single band by sodium dodecyl sulfate-polyacrylamide gel electrophoresis using affinity chromatography. When the phosphatase was allowed to react with 32P-labeled substrates and then rapidly denaturated, a 32P-labeled phosphoprotein could be visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Transient formation of a 32P-labeled phosphoprotein was observed, and the 32P-labeled protein disappeared as substrate was consumed. In the presence of 32P-labeled p-nitrophenyl phosphate, 0.27 mol of phosphate was incorporated per mol of protein-tyrosine-phosphatase. Site-directed mutagenesis of a catalytically essential cystine residue (position 215) in the recombinant protein resulted in an inactive enzyme, and no phosphoprotein was formed. The 32P-labeled phosphoprotein showed a maximum lability between pH 2.5 and 3.5 and was rapidly decomposed in the presence of iodine. These properties, along with additional site-directed mutations, suggest that the protein-tyrosine-phosphatase forms a covalent thiol phosphate linkage between Cys215 and phosphate.     

Genetic diversity and restoration of a recalcitrant clonal sedge (Tetraria capillaris Cyperaceae)

The genetic diversity of a clonal sedge (Tertraria capillaris) was assessed using isozyme analysis of 11 loci. Of 29 enzyme systems tested, eight were selected which gave interpretable bands with consistently good resolution. Though seedlings of the species are rarely observed in nature, isozyme analysis showed that for the study transects containing 100 sample plants, the majority of plants at the site were sexually rather than clonally derived. Young plants generated from embryos grown in vitro from excised seeds showed a high level of genetic diversity which could account for the genetic diversity measured in the parent population. In terms of restoration of the species, 85% of the assessed genetic diversity at the study site could be retained if 25 T. capillaris plants were taken at random. The study illustrates how genetic assessment coupled with tissue culture methods provides a feasible model for the recovery of most of the assessed local genetic diversity of a clonal species.     

Identification of the human YVH1 protein-tyrosine phosphatase orthologue reveals a novel zinc binding domain essential for in vivo function.

A human orthologue of the Saccharomyces cerevisiae YVH1 protein-tyrosine phosphatase is able to rescue the slow growth defect caused by the disruption of the S. cerevisiae YVH1 gene. The human YVH1 gene is located on chromosome 1q21-q22, which falls in a region amplified in human liposarcomas. The evolutionary conserved COOH-terminal noncatalytic domain of human YVH1 is essential for in vivo function. The cysteine-rich COOH-terminal domain is capable of coordinating 2 mol of zinc/mol of protein, defining it as a novel zinc finger domain. Human YVH1 is the first protein-tyrosine phosphatase that contains and is regulated by a zinc finger domain.     

Effect of emigration on cannibalism and intraguild predation in aphidophagous ladybirds

Abstract.  1. The incidence and timing of emigration, cannibalism, and intraguild predation of larvae of three aphidophagous ladybirds (Coleoptera: Coccinellidae), Harmonia axyridis Pallas, Coccinella septempunctata brucki Mulsant, and Propylea japonica Mulsant, relative to the presence of prey was determined in the laboratory in single- and mixed-species populations.
2. In single-species populations, 80% of the larvae of C. s. brucki emigrated prior to the extinction of the aphid population and no larvae were lost due to cannibalism; however > 80% of the larvae of the other two species were still present when the aphid became extinct and the losses due to cannibalism for H. axyridis and P. japonica were 25% and 14% respectively. Finally, 28% of the P. japonica larvae completed their development, whereas no larvae of the other two species became adult.
3. In mixed-species populations, mortality of P. japonica attributable to cannibalism or intraguild predation increased greatly to 60%, whereas that of the other two species remained about the same. Consequently, survival of H. axyridis larvae improved and survival of P. japonica worsened; however the survival of C. s. brucki larvae was not affected by the other two species. Early emigration by C. s. brucki larvae may have enabled them to escape intraguild predation by H. axyridis in this system.