Applications of Background Data in Ecological Risk Assessment: Various Shades of Gray

This paper discusses general approaches for evaluating the utility and manner of conducting background analyses in soil for ecological risk assessments. The types and sources of background data are discussed, and advantages and disadvantages of using literature-based versus site-specific background data are presented. The value of background evaluations is discussed with regard to the goals and objectives for a project. A comparison of literature-based ecological soil screening levels with generic metal background concentrations is presented to illustrate a typical problem in incorporating background data in ecological risk assessments, which is that many generic background concentrations are higher than ecological screening levels. This brings into question both the relevance of ecological screening levels and generic background levels. These issues are discussed along with cost-benefit considerations in an attempt to provide recommendations for determining the most appropriate type of background evaluation to conduct at a given site.     

Electroporation and Microinjection Successfully Deliver Single-Stranded and Duplex DNA into Live Cells as Detected by FRET Measurements

Förster resonance energy transfer (FRET) technology relies on the close proximity of two compatible fluorophores for energy transfer. Tagged (Cy3 and Cy5) complementary DNA strands forming a stable duplex and a doubly-tagged single strand were shown to demonstrate FRET outside of a cellular environment. FRET was also observed after transfecting these DNA strands into fixed and live cells using methods such as microinjection and electroporation, but not when using lipid based transfection reagents, unless in the presence of the endosomal acidification inhibitor bafilomycin. Avoiding the endocytosis pathway is essential for efficient delivery of intact DNA probes into cells.     

The effect of antimycin a on carotenogenesis in Verticillium agaricinum

Summary Antimycin A did not induce carotenogenesis in dark grown cultures of V. agaricinum, but total protein was increased. In light, antimycin A did not affect total carotenoids, although protein was slightly increased. The results suggest that antimycin A could not have acted here as an inducer for the synthesis of specific carotenogenic enzymes or by inactivating a repressor as has been suggested for certain bacteria.     

Mechanism of action of developmentally regulated sea urchin inhibitor of eIF-4

The developmentally regulated inhibitor of eIF-4 function found in unfertilized sea urchin eggs has been partially purified and its mechanism of action studied in vitro using purified recombinant eIF-4α and cell-free translation systems. The results demonstrate that although the phosphorylation of eIF-4α is necessary to promote protein synthesis, it is not sufficient to maintain all aspects of eIF-4 function. The egg inhibitor does not change eIF-4α phosphorylation state. During the blockage of initiation caused by the egg inhibitor, eIF-4α remains phosphorylated but accumulates in a 48S initiation intermediate. This suggests that the egg inhibitor functions by preventing the release of eIF-4α from the small ribosomal subunit. The characteristics of the inhibitor in a reticulocyte translation system demonstrate that eIF-4 activity is inhibited within 3–6 min. However, the inhibitor's characteristics in a mRNA-dependent translation system contrast with this. Preincubation with the inhibitor for 5–25 min prior to the addition of mRNA does not prevent endogenous eIF-4 from participating in translation but diminishes its ability to be reutilized, consistent with the accumulation of eIF-4α on the small ribosomal subunit. The ribosomal localization of the inhibitor suggests that it could prevent eIF-4α release by direct binding. The gradual inactivation of the inhibitor following fertilization indicates that it represents a component of a novel regulatory cascade that modulates eIF-4 activity. © 1993 Wiley-Liss, Inc.