Characterization of an E. coli mutant with a thermolabile initiation factor IF3 activity.

Summary A thermosensitive E. coli mutant is described which has at least two defects in vitro: a thermolabile initiation factor IF3 activity and a modified L-phenylalanine: tRNA^Phe ligase (EC 6.1.1.20) activity. These two defects cotransduce and are located near 38 min on the new E. coli map. Thermoresistant revertants showing in vitro reversion for one defect also revert in vitro for the other defect. The thermosensitive mutation is recessive to its wild type allele, and in vitro analysis of wild type/mutant heterodiploïds also show reversion for both defects.     

Distinct restriction of complement- and cell-mediated lysis

Complement- and cell-mediated killing utilize related effector proteins (C8/C9 and perforin, respectively), suggesting that proteins which protect cells against complement- and cell-mediated attack may also be similar. In homologous complement-mediated killing two protective proteins, which are anchored to the cell membrane by phosphatidylinositol glycan (PIG) tails, are known. To study whether similar PIG-tailed proteins protect against lymphocyte-mediated killing, nucleated cell lines with a mutation in the biosynthesis of the PIG anchor were used. It was found that PIG-tailed membrane proteins restrict homologous complement-mediated lysis but not three different types of cell-mediated killing or lysis by purified perforin. Furthermore, E from patients with an acquired defect in PIG tail biosynthesis did not differ from normal E in sensitivity to antibody-dependent cell-mediated cytotoxicity, in spite of their increased sensitivity to human C8 and C9.     

Utilizing in silico and in vitro methods to identify possible binding sites of a novel ligand against Pseudomonas aeruginosa phospholipase toxin ExoU

Multi-drug resistant infections caused by the opportunistic pathogen, Pseudomonas aeruginosa (P. aeruginosa), are a continuing problem that contribute to morbidity and mortality in immunocompromised hosts such as cystic fibrosis (CF), wound and burn patients. The bacterial toxin ExoU is one of four potent toxins that P. aeruginosa secretes into the epithelial cells of hosts. In this study, NMR Saturation Transfer Difference (STD) and in silico Schrödinger Computational Modeling were used to identify a possible binding site of a novel ligand methoctramine targeting ExoU. Future project goals will be to design a structure activity relationship (SAR) study of methoctramine and ExoU and lead to a new drug solving ExoU toxicity P. aeruginosa exerts in the clinical environment.     

Longitudinal variation in zooplankton δ13C through the Northwest Passage: inference for incorporation of sea-ice POM into pelagic foodwebs

Previous research has demonstrated a west-to-east decrease in zooplankton δ¹³C along the Alaskan coast. We extended the transect into the Canadian Arctic archipelago through the Northwest Passage in order to investigate whether this longitudinal gradient persists eastward. Contrary to the previous observations, zooplankton δ¹³C was found to be essentially invariate, despite a sampling survey length double that of the earlier studies. This resulted from zooplankton at the coldest and ice-bound stations being found to be enriched in ¹³C relative to what would be expected from the ambient water temperatures and calculated [CO₂aq]. We suggest that this was due to the assimilation of ice POM which, as has been demonstrated for other forms of benthic algae, is enriched in ¹³C due to restraints on boundary layer diffusion. The present results therefore support other traditional, non-isotope research in suggesting that ice-bound polar foodwebs may be examples of aquatic systems where there is a functional energy connectivity between the attached and openwater environments. Received: 21 January 1998 / Accepted: 27 April 1998