Inhibition of Membrane-Active Peptides by Fatty Acid–Peptide Hybrids

Nine fatty acid–peptide hybrid molecules were constructed using the general formula CH₃(CH₂) _n CO-Phe Asp Cys-amide and tested for their ability to inhibit cell lysis induced by the membrane-active peptide melittin. All of these molecules, where n = 4–14, inhibited the action of melittin to some extent, but the longer carbon chains were most effective. Several potential inhibitors were also constructed with conservative substitutions in the peptide portion of the molecule. All were effective to varying degrees. We concluded that in the hexapeptide inhibitor published by Blondelle et al. (1993), the role of the first three residues is only to provide hydrophobic interaction with the melittin and has no particular amino acid sequence specificity. Some of these inhibitors were found to inhibit the lytic activity of a melittin analogue which had only superficial sequence similarity to melittin and also a truncated form of melittin, indicating the generality of the action of the inhibitors.Deceased 5/4/98     

Evolutionary rescue by beneficial mutations in environments that change in space and time

A factor that may limit the ability of many populations to adapt to changing conditions is the rate at which beneficial mutations can become established. We study the probability that mutations become established in changing environments by extending the classic theory for branching processes. When environments change in time, under quite general conditions, the establishment probability is approximately twice the ‘effective selection coefficient’, whose value is an average that gives most weight to a mutant''s fitness in the generations immediately after it appears. When fitness varies along a gradient in a continuous habitat, increased dispersal generally decreases the chance a mutation establishes because mutations move out of areas where they are most adapted. When there is a patch of favourable habitat that moves in time, there is a maximum speed of movement above which mutations cannot become established, regardless of when and where they first appear. This critical speed limit, which is proportional to the mutation''s maximum selective advantage, represents an absolute constraint on the potential of locally adapted mutations to contribute to evolutionary rescue.     

Immunologic effects of interleukin 2 in primary immunodeficiency diseases

Five children with primary deficiencies of T cell function were studied to assess the effects of highly purified exogenous Interleukin 2 (IL 2) on their in vitro T cell responses. The lymphocytes from one child with Nezelof's T cell deficiency demonstrated absence of endogenous IL 2 production and improved proliferative responses to mitogen or alloantigen in the presence of exogenous IL 2. Moreover, during in vitro mixed lymphocyte culture in the presence of exogenous IL 2, his lymphocytes were able to develop into cytotoxic effector cells. A second child with Nezelof's syndrome demonstrated a different type of defect. The lymphocytes from this child had less impairment of endogenous IL 2 production. Although IL 2 increased the proliferation of his cells in response to PHA, similar augmentation was not seen after stimulation with OKT3 or alloantigen. In cell-mediated cytotoxicity assays, after mixed lymphocyte culture, natural killer-like activity was strongly boosted in the cultures that contained IL 2, but T cell-mediated cytotoxicity was not. The lymphocytes from three patients with severe combined immunodeficiency did not show improved proliferative responses in the presence of IL 2. Thus, only one of the five patients demonstrated the combination of defective endogenous IL 2 production, but preservation of the ability to respond appropriately to exogenous IL 2. This child may therefore have suffered from a T cell defect pathophysiologically similar to that seen in nude or aged mice.     

Salmonella spp. in nestling common barn-owls (Tyto alba) from southwestern New Jersey

The prevalence of Salmonella spp. in nestling common barn-owls was investigated in southwestern New Jersey during the summer of 1985. Of 94 owls sampled by swabbing the cloaca, eight (8.5%) were found to harbor Salmonella spp. Three serotypes--S. thompson, S. tuindorp, and S. typhimurium--were identified. Five (20%) of the 25 nest sites examined (all of them in or near farm buildings or dwellings) contained Salmonella-positive owls.     

Frequent mowing is better than grazing for the conservation value of lowland tussock grasssland at Pontville,Tasmania

Abstract The effects of an unusual high frequency mowing regime, which involved the removal of slash, were compared to moderate grazing through the method of paired quadrats across a fenceline, which was orthogonal to a weak environmental gradient. The mown plots proved superior in their conservation characteristics to the moderately grazed plots. The mowing regime produced greater cover of rare or threatened species, greater native cover and lesser exotic grass cover. It thus presents an opportunity for maintaining or improving the condition of previously grazed remnants in reserves without resorting to the use of stock or fire for biomass reduction.     

The influence of prenatal and postnatal fraternity size on reproduction in mice

Effects of prenatal and postnatal fraternity size (size of litter in which an individual is reared) on age at vaginal opening, growth, and subsequent litter production were examined by rearing mice in standardized prenatal and postnatal fraternities in a 3 X 3 factorial design. Prenatal fraternity size was standardized by reducing litters of 14 or more to either 14, 10, or 6 fetuses on Day 9 of gestation. Postnatal fraternity size was standardized by assigning pups randomly to nurse in litters of 5, 10, or 15 pups within 24 h of birth. Both prenatal and postnatal fraternity size affected growth of the mice (p = 0.02 and p less than 0.01, respectively) with mice reared in small fraternities attaining greater weights throughout the study. Prenatal fraternity size had a negative linear effect on litter size at second parity and tended to have a positive linear effect on age at vaginal opening. Postnatal fraternity size affected age at vaginal opening (p less than 0.01), litter size at first parity (p less than 0.01), and litter size at second parity (p = 0.03). These effects were positive and linear for age at vaginal opening (p less than 0.01; small fraternity size associated with younger age at vaginal opening) and negative and linear for litter size at first and second parity (p less than 0.01 and p = 0.10, respectively; smaller fraternity size associated with larger litter size). There was no interaction between prenatal and postnatal fraternity size effects on age at vaginal opening or litter size (p greater than 0.20).     

RNA-DNA hybridization promoted by E. coli RecA protein.

RecA protein of E. coli plays a central regulatory role that is induced by damage to DNA and results in the inactivation of LexA repressor. In vitro, RecA protein binds preferentially to single-stranded DNA to form a nucleoprotein filament that can recognize homology in naked duplex DNA and promote extensive strand exchange. Although RecA protein shows little tendency at neutral pH to bind to RNA, we found that it nonetheless catalyzed at 37 degrees C the hybridization of complementary RNA and single-stranded DNA sequences. Hybrids made by RecA protein at 37 degrees C appeared indistinguishable from ones prepared by thermal annealing. RNA-DNA hybridization by RecA protein at neutral pH required, as does RecA-promoted homologous pairing, optimal conditions for the formation of RecA nucleoprotein filaments. The cosedimentation of RNA with those filaments further paralleled observations made on the formation of networks of nucleoprotein filaments with double-stranded DNA, an instrumental intermediate in homologous pairing in vitro. These similarities with the pairing reaction support the view that RecA protein acts specifically in the hybridization reaction.     

Effect of polydimethylsiloxane oxygen carriers on the biological bleaching of hardwood kraft pulp by Trametes versicolor

Summary Improving the availability of oxygen by adding polydimethylsiloxanes (PDMS) oxygen carriers to Trametes versicolor cultures increased pulp brightening. The presence of the oxygen carriers in cultures of T. versicolor with hardwood kraft pulp increased the growth rate of the fungus, but not the ultimate biomass yield. The PDMS also stimulated brightening of hardwood kraft pulp by it T. versicolor immobilized in polyurethane foam. A threefold increase in the oxygen uptake rate in T. versicolor cultures with PDMS was observed. This increase can be explained by elevated oxygen transfer rate and attributed to the surfactant properties of PDMS. Offprint requests to: E. ZiomekIssued as NRCC 32760