Isolation of viral coat protein mutants with altered assembly and aggregation properties

A method was developed to screen bacteria for synthesis of mutant proteins with altered assembly and solubility properties using bacteriophage MS2 coat protein as a model self-associating protein. Colonies expressing coat protein from a plasmid were covered with an agarose overlay under conditions that caused the lysis of some of the cells in each colony. The proteins thus liberated diffused through the overlay at rates depending on their molecular sizes. After transfer of the proteins to a nitrocellulose membrane, probing with coat protein-specific antiserum revealed spots whose sizes and intensities were related to the aggregation state of coat protein. The method was employed in the isolation of assembly defective mutants and to find soluble variants of an aggregation-prone coat protein mutant.     

Copper- and arsenate-induced oxidative stress in Holcus lanatus L. clones with differential sensitivity

The biochemical responses of Holcus lanatus L. to copper and arsenate exposure were investigated in arsenate‐tolerant and ‐non‐tolerant plants from uncontaminated and arsenic/copper‐contaminated sites. Increases in lipid peroxidation, superoxide dismutase (SOD) activity and phytochelatin (PC) production were correlated with increasing copper and arsenate exposure. In addition, significant differences in biochemical responses were observed between arsenate‐tolerant and ‐non‐tolerant plants. Copper and arsenate exposure led to the production of reactive oxygen species, resulting in significant lipid peroxidation in non‐tolerant plants. However, SOD activity was suppressed upon metal exposure, possibly due to interference with metallo‐enzymes. It was concluded that in non‐tolerant plants, rapid arsenate influx resulted in PC production, glutathione depletion and lipid peroxidation. This process would also occur in tolerant plants, but by decreasing the rate of influx, they were able to maintain their constitutive functions, detoxify the metals though PC production and quench reactive oxygen species by SOD activity.     

Molecular Mechanisms of Translation Initiation in Mammals Studied by in vitroReconstruction of Initiation Complexes

Papers on the mechanisms of translation initiation in mammals studied by reconstruction of initiation complexes from individual components are reviewed. The author points to the constraints of this approach and to the pitfalls ignoring which one might come to erroneous conclusions and even artifacts. In addition, some methods employed in the field as well as some technical problems are discussed in the paper, together with the means of obviating them. The review could be a guidebook for newcomers into this quite labor-consuming field.     

Levels of genetic polymorphism: marker loci versus quantitative traits.

Species are the units used to measure ecological diversity and alleles are the units of genetic diversity. Genetic variation within and among species has been documented most extensively using allozyme electrophoresis. This reveals wide differences in genetic variability within, and genetic distances among, species, demonstrating that species are not equivalent units of diversity. The extent to which the pattern observed for allozymes can be used to infer patterns of genetic variation in quantitative traits depends on the forces generating and maintaining variability. Allozyme variation is probably not strictly neutral but, nevertheless, heterozygosity is expected to be influenced by population size and genetic distance will be affected by time since divergence. The same is true for quantitative traits influenced by many genes and under weak stabilizing selection. However, the limited data available suggest that allozyme variability is a poor predictor of genetic variation in quantitative traits within populations. It is a better predictor of general phenotypic divergence and of postzygotic isolation between populations or species, but is only weakly correlated with prezygotic isolation. Studies of grasshopper and planthopper mating signal variation and assortative mating illustrate how these characters evolve independently of general genetic and morphological variation. The role of such traits in prezygotic isolation, and hence speciation, means that they will contribute significantly to the diversity of levels of genetic variation within and among species.     

Cell wall polysaccharides are informative in Porphyra species taxonomy

As part of systematic studies of the genus Porphyrain New Zealand, constituent sugar analyses of cell wall polysaccharidesin situ in dry thalli were found to yield data that weretaxonomically informative. Variation in constituent sugar levels betweenspecieswas sufficient in some cases to be useful in species differentiation. Thereproductive state of thallus regions had a significant impact on the levels ofconstituent sugars, whereas storage of dried thalli for eight months had noeffect. Three epiphytic taxa currently classified as species ofPorphyra appear to be incorrectly placed within the genus,as their constituent sugars and the levels of these sugars differed markedlyfrom those of all other species examined.     

Peanut (Arachis hypogaea) lectin recognizes α-linked galactose, but not N-acetyl lactosamine in N-linked oligosaccharide terminals

Peanut (Arachis hypogaea) agglutinin (PNA) is extensively used as tumour marker as it strongly recognises the cancer specific T antigen (Galβ1→3GalNAc-), but not its sialylated version. However, an additional specificity towards Galβ1→4GlcNAc (LacNAc), which is not tumour specific, had been attributed to PNA. For correct interpretation of lectin histochemical results we examined PNA sugar specificity using naturally occurring or semi-synthetic glycoproteins, matrix-immobilised galactosides and lectin-binding tissue glycoproteins, rather than mono- or disaccharides as ligands. Dot-blots, transfer blots or polystyrene plate coatings of the soluble glycoconjugates were probed with horse-radish peroxidase (HRP) conjugates of PNA and other lectins of known specificity. Modifications of PNA-binding glycoproteins, including selective removal of O-linked oligosaccharides and treatment with glycosidases revealed that Galβ1→4GlcNAc (LacNAc) was ineffective while terminal α-linked galactose (TAG) as well as exposed T antigen (Galβ1→3 GalNAc-) was excellent as sugar moiety in glycoproteins for their recognition by PNA. When immobilised, melibiose was superior to lactose in PNA binding. Results were confirmed using TAG-specific human serum anti-α-galactoside antibody.     

Phylogenetic evidence for multiple losses of a sexually selected character in phrynosomatid lizards

The evolution of conspicuous male display ornaments is a common trend in diverse groups of organisms and a continuing challenge to studies of sexual selection. A phylogenetic approach was used to examine macro-evolutionary patterns of change in sexually dichromatic display coloration (distinctively coloured belly patches) among 130 taxa of phrynosomatid lizards. The results showed repeated losses of sexual dimorphism, which occur through losses of conspicuous male coloration or gains of conspicuous female coloration. The frequent loss of male traits is surprising, given that sexual selection presumably drives their evolutionary origin and maintenance, but is consistent with a recently proposed hypothesis suggesting that females may lose responsiveness to male traits over macro-evolutionary time-scales. The observation of repeated losses of male traits in phrynosomatid lizards (and other groups) may have implications for testing among competing models for the evolution of female preferences. A concentrated changes test showed that changes in male display coloration are significantly associated with the use of ground-dwelling habitat, as opposed to rock- or tree-dwelling habitats. This result suggests a role for natural selection in the loss of male display traits in phrynosomatid lizards, but habitat type alone may be insufficient to explain these losses.