Degradation products of the mRNA encoding the small subunit of ribulose-1,5-bisphosphate carboxylase in soybean and transgenic petunia.

The degradation of a soybean ribulose-1,5-bisphosphate carboxylase small subunit RNA, SRS4, was investigated in soybean seedlings and in petunia plants transformed with an SRS4 gene construct. Polyacrylamide RNA gel blot, primer extension, and S1 nuclease analyses were used to identify and map fragments of the SRS4 mRNA generated in vivo. We showed that SRS4 mRNA is degraded to a characteristic set of fragments in soybean and transgenic petunia and that degradation is not dependent on position of insertion of the gene construct within the genome, on the expression level of the SRS4 mRNA, or on the rbcS promoter. Degradation products lacked poly(A) tails and fractionated with poly(A)-depleted RNA on oligo(dT)-sepharose columns. These products pelleted with polysomes and were released from polysomes prepared with EDTA. Sequences at the 5' end of the SRS4 mRNA were more stable than those at the 3' end of the mRNA. Three models for SRS4 mRNA degradation involving endonucleolytic and exonucleolytic degradation were presented to explain the origin of the 5' proximal fragments.     

Localization of profilin- and actin-like immunoreactivity in in vitro-germinated tobacco pollen tubes by electron microscopy after special water-free fixation techniques

Double immunogold labeling of profilin and actin was performed on ultrathin sections of in vitro germinated tobacco pollen using different anti-profilin and anti-actin antibodies. Since profilin, besides its role as an actin-binding protein, is known as an allergen, water-free fixation in p-formaldehyde vapor was used. Profilin labeling occurs throughout the cytoplasm of the pollen tube. There is no profilin in the pollen tube wall. Actin reactivity is found in the cytoplasm and extracellularly in the pollen tube wall where three out of four different anti-actin antibodies give a positive signal. This labeling of the pollen tube wall may result from a wall-bound actin, an isoform of actin not yet described or from the presence of a molecule immunologically indistinguishable from actin.     

Protein expression in E. coli minicells by recombinant plasmids.

The polypeptides synthesized in E. coli minicells from recombinant plasmids containing DNA fragments from cauliflower mosaic virus, Drosophila melanogaster, and mouse mitochondria were examined. Molecularly cloned fragments of cauliflower mosaic virus DNA directed the synthesis of high levels of three polypeptides, which were synthesized entirely from within the cloned virus DNA fragments independent of their insertion into the plasmid vehicles. Several fragments of D. melanogaster DNA were capable of initiating polypeptide synthesis; however, termination of these polypeptides was dependent upon the insertion into the plasmid vehicle. The majority of D. melanogaster DNA fragments examined did not direct the detectable synthesis of any polypeptides. Insertion of DNA into the Eco RI site of ColE1 and pSC101 plasmids resulted in the altered expression of plasmid-encoded polypeptides. In the case of ColE1, this site of insertion lies within the colicin E1 structural gene, and insertion of foreign DNA into the site results in the synthesis of an inactive truncated colicin E1 molecule. It is probable that the Eco RI site in pSC101 lies within the structural gene for a polypeptide involved in tetracycline resistance, and insertion of DNA into this site may also result in the synthesis of a truncated or elongated polypeptide.     

Enhancement of protein secretion in Pichia pastoris by overexpression of protein disulfide isomerase

A potential vaccine candidate, Necator americanus secretory protein (Na-ASP1), against hookworm infections, has been expressed in Pichia pastoris. Na-ASP1, a 45 kDa protein containing 20 cysteines, was directed outside the cell by fusing the protein to the preprosequence of the alpha-mating factor of Saccharomyces cerevisiae. Most of the protein produced by single copy clones was secreted outside the cell. However, increasing gene copy number of Na-ASP1 protein in P. pastoris saturated secretory capacity and therefore, decreased the amount of secreted protein in clones harboring multiple copies of Na-ASP1 gene. Overexpression of the endoplasmic reticulum (ER) resident, homologous chaperone protein, protein disulfide isomerase (PDI) was able to increase the secretion of (Na-ASP1) protein in high copy clones. The effect of PDI levels on secretion of Na-ASP1 protein was examined in clones with varying copy number of PDI gene. Increase in secreted Na-ASP1 secretion is correlated well with the PDI copy number. Increasing levels of PDI also increased overall Na-ASP1 protein production in all the clones. Nevertheless, there was still accumulation of intracellular Na-ASP1 protein in P. pastoris clones over-expressing Na-ASP1 and PDI proteins.     

Enhanced tolerance to and accumulation of mercury, but not arsenic, in plants overexpressing two enzymes required for thiol peptide synthesis

Arsenic and mercury are among the most toxic elemental pollutants in the environment, endangering human health and ecological integrity. Both elements are found in highly thiol-reactive forms, arsenite and Hg(II), respectively, in plant tissues. Overexpression of Escherichia coli γ-glutamylcysteine synthetase (ECS) or glutathione synthetase (GS) in Arabidopsis thaliana plants provided significant increases in the thiol peptides glutathione (GSH) and γ-glutamylcysteine (γ-EC), and/or phytochelatins (PCs), and some resistance to arsenic and mercury, but no substantial increases in the levels of these elements in above-ground tissues. In contrast, the co-expression of ECS and GS in ECS × GS lines produced significant increases in tolerance to toxic levels of mercury. The ECS × GS co-expression line accumulated 35-fold more biomass and three-fold more mercury aboveground than the wild type (WT) when grown on Hg(II). No increases in arsenic accumulation were detected in the ECS × GS line. Increased resistance to and accumulation of mercury apparently resulted from enhanced root concentrations of PCs in ECS × GS co-expression lines not seen in the wild type or lines expressing ECS or GS alone. Correlations between the levels of arsenic and mercury resistance and accumulation and increases in the accumulation of the various thiol peptides in the ECS, GS and ECS × GS transgenic plant lines are discussed.