Spectroscopic, thermodynamic and kinetic properties of Candida nitratophila nitrate reductase.

HL-60 cells possess a 60 kDa Ca2(+)-binding protein that is contained in a discrete subcellular compartment, referred to as calciosomes. Subcellular fractionation studies have suggested that, in HL-60 cells, this intracellular compartment is an Ins(1,4,5)P3-sensitive Ca2+ store. In order to investigate the structural relationship of the 60 kDa Ca2(+)-binding protein of HL-60 cells to other Ca2(+)-binding proteins, we have purified the protein by ammonium sulphate extraction, acid precipitation, and DEAE-cellulose and phenyl-Sepharose column chromatography. The N-terminal sequence of the protein shows 93% identity with rabbit muscle calreticulin, a recently cloned sarcoplasmic reticulum Ca2(+)-binding protein. No amino acid sequence similarity with calsequestrin was found, although the purified protein cross-reacted with anti-calsequestrin antibodies. The calreticulin-related protein of HL-60 cells might play a role as an intravesicular Ca2(+)-binding protein of an Ins(1,4,5)P3-sensitive Ca2+ store.     

Growth suppression in early-stationary-phase nutrient broth cultures of Salmonella typhimurium and Escherichia coli is genus specific and not regulated by sigma S.

We have studied the growth suppression seen in early-stationary-phase LB broth cultures of Salmonella typhimurium. Multiplication of small numbers of an antibiotic-resistant S. typhimurium mutant was prevented when the mutant was added to 24-h cultures of the antibiotic-sensitive parent strain, whereas an antibiotic-resistant mutant of an Escherichia coli strain added to the same culture grew well. A 24-h E. coli culture produced a similar specific bacteriostatic inhibition against E. coli. In older cultures, a specific bactericidal effect similar to that observed by M. M. Zambrano and R. Kolter (J. Bacteriol. 175:5642-5647, 1993) was also observed. Whether incubated statically or shaken, sufficient nutrients were present in the filtered supernatants of 24-h cultures for small inocula of the same strain to multiply to ca. 10(9) CFU/ml after reincubation. Introduction of the rpoS mutation had no effect on the specific bacteriostatic inhibition. Similar specific inhibition was also observed in strains of Citrobacter freundii, Klebsiella pneumoniae, Enterobacter agglomerans, and Shigella spp. Experiments in which the 24-h culture was physically separated from the antibiotic-resistant mutant by using a dialysis membrane were carried out. These results indicated that the inhibition might be mediated by a diffusible but labile chemical mediator.     

Activation of Protein Kinase C Augments Peptide Release from Rat Sensory Neurons

Abstract: To determine whether protein kinase C (PKC) mediates release of peptides from sensory neurons, we examined the effects of altering PKC activity on resting and evoked release of substance P (SP) and calcitonin gene-related peptide (CGRP). Exposing rat sensory neurons in culture to 10 or 50 n M phorbol 12,13-dibutyrate (PDBu) significantly increased SP and CGRP release at least 10-fold above resting levels, whereas the inactive 4α-PDBu analogue at 100 n M had no effect on release. Furthermore, 100 n M bradykinin increased peptide release approximately fivefold. Down-regulation of PKC significantly attenuated the release of peptides evoked by either PDBu or bradykinin. PDBu at 1 n M or 1-oleoyl-2-acetyl- sn -glycerol at 50 µ M did not alter resting release of peptides, but augmented potassium- and capsaicin-stimulated release of both SP and CGRP approximately twofold. This sensitizing action of PKC activators on peptide release was significantly reduced by PKC down-regulation or by pretreating cultures with 10 n M staurosporine. These results establish that activation of PKC is important in the regulation of peptide release from sensory neurons. The PKC-induced enhancement of peptide release may be a mechanism underlying the neuronal sensitization that produces hyperalgesia.     

Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves

A puzzling population-genetic phenomenon widely reported in allozyme surveys of marine bivalves is the occurrence of heterozygote deficits relative to Hardy-Weinberg expectations. Possible explanations for this pattern are categorized with respect to whether the effects should be confined to protein-level assays or are genomically pervasive and expected to be registered in both protein- and DNA-level assays. Anonymous nuclear DNA markers from the American oyster were employed to reexamine the phenomenon. In assays based on the polymerase chain reaction (PCR), two DNA-level processes were encountered that can lead to artifactual genotypic scorings: (a) differential amplification of alleles at a target locus and (b) amplification from multiple paralogous loci. We describe symptoms of these complications and prescribe methods that should generally help to ameliorate them. When artifactual scorings at two anonymous DNA loci in the American oyster were corrected, Hardy-Weinberg deviations registered in preliminary population assays decreased to nonsignificant values. Implications of these findings for the heterozygote-deficit phenomenon in marine bivalves, and for the general development and use of PCR-based assays, are discussed.      

Erythropoietin and interleukin-2 activate distinct JAK kinase family members.

The erythropoietin (EPO) receptor and the interleukin-2 (IL-2) receptor beta-chain subunit are members of the cytokine receptor superfamily. They have conserved primary amino acid sequences in their cytoplasmic domains and activate phosphorylation of common substrates, suggesting common biochemical signaling mechanisms. We have generated a cell line, CTLL-EPO-R, that contains functional cell surface receptors for both EPO and IL-2. CTLL-EPO-R cells demonstrated similar growth kinetics in EPO and IL-2. Stimulation with EPO resulted in the rapid, dose-dependent tyrosine phosphorylation of JAK2. In contrast, stimulation with IL-2 or the related cytokine IL-4 resulted in the rapid, dose-dependent tyrosine phosphorylation of JAK1 and an additional 116-kDa protein. This 116-kDa protein was itself immunoreactive with a polyclonal antiserum raised against JAK2 and appears to be a novel member of the JAK kinase family. Immune complex kinase assays confirmed that IL-2 and IL-4 activated JAK1 and EPO activated JAK2. These results demonstrate that multiple biochemical pathways are capable of conferring a mitogenic signal in CTLL-EPO-R cells and that the EPO and IL-2 receptors interact with distinct JAK kinase family members within the same cellular background.     

Causal inference and large-scale expert validation shed light on the drivers of SDM accuracy and variance

Aim

To develop a causal understanding of the drivers of Species distribution model (SDM) performance.

Location

United Kingdom (UK).

Methods

We measured the accuracy and variance of SDMs fitted for 518 species of invertebrate and plant in the UK. Our measure of variance reflects variation among replicate model fits, and taxon experts assessed model accuracy. Using directed acyclic graphs, we developed a causal model depicting plausible effects of explanatory variables (e.g. species' prevalence, sample size) on SDM accuracy and variance and quantified those effects using a multilevel piecewise path model.

Results

According to our model, sample size and niche completeness (proportion of a species' niche covered by sampling) directly affect SDM accuracy and variance. Prevalence and range completeness have indirect effects mediated by sample size. Challenging conventional wisdom, we found that the effect of prevalence on SDM accuracy is positive. This reflects the facts that sample size has a positive effect on accuracy and larger sample sizes are possible for widespread species. It is possible, however, that the omission of an unobserved confounder biased this effect. Previous studies, which reported negative correlations between prevalence and SDM accuracy, conditioned on sample size.

Main conclusions

Our model explicates the causal basis of previously reported correlations between SDM performance and species/data characteristics. It also suggests that niche completeness has similarly large effects on SDM accuracy and variance as sample size. Analysts should consider niche completeness, or proxies thereof, in addition to sample size when deciding whether modelling is worthwhile.     

Peatlands as scientific archives of past biodiversity

Peat bogs preserve past biodiversity in a way which is unique among ecosystems, but the full realization of this, and the exploitation of the various records which are archived in the stratified layers of peat, is only now beginning. Present knowledge of peat formation in ombrotrophic or rain-fed bogs is reviewed and the many advantages of such systems as proxy-data sources are summarized. Some results of recent work involving pollen analysis and human impact, pollution histories, volcanic ash layers, plant macrofossils and the prospects for a detailed proxy-climate record are presented. The present vegetation of such bogs is only a very partial view of their past biodiversity; the conservation of the peat that remains must have a high priority.     

The impact of insecticide resistance in the currant-lettuce aphid, Nasonovia ribisnigri, on pest management in lettuce

Abstract 1 This paper reports on experiments to determine how two different insecticide resistance phenotypes in the aphid Nasonovia ribisnigri (Mosley), which is a major pest of lettuce, change its susceptibility to pyrethroid insecticides and the carbamate pirimicarb. 2 A novel statistical approach determined how the effectiveness of different insecticides was changed by the two resistance phenotypes. This compared the between‐plant distribution of aphid numbers, as opposed to the mean number of aphids per plant. 3 Results from field cage experiments showed that the effect of the resistances differed. Pyrethroid resistance resulted in lower mortality immediately after application of pyrethroids, whereas resistance to pirimicarb shortened the time over which the chemical was effective. 4 The results of laboratory bioassays suggested that these two resistances were not found together in N. ribisnigri. However, the results reported here contradict this assertion. 5 Experiments with insecticide residues showed that reproduction of resistant N. ribisnigri was greater than that of susceptible N. ribisnigri on plants with ageing insecticide residues, even in circumstances where mortality of resistant and susceptible clones of N. ribisnigri were similar. 6 If more than a few aphids are found on a plant then a whole consignment can be rejected for processing. The results reported here suggest that the effect of both insecticide resistances in N. ribsinigri will be to increase the proportion of lettuce heads with an unacceptable number of aphids on them, leading to increased rejection of plants for processing.