Structural modeling and mutational analysis of yeast eukaryotic translation initiation factor 5A reveal new critical residues and reinforce its involvement in protein synthesis

Eukaryotic translation initiation factor 5A (eIF5A) is a protein that is highly conserved and essential for cell viability. This factor is the only protein known to contain the unique and essential amino acid residue hypusine. This work focused on the structural and functional characterization of Saccharomyces cerevisiae eIF5A. The tertiary structure of yeast eIF5A was modeled based on the structure of its Leishmania mexicana homologue and this model was used to predict the structural localization of new site-directed and randomly generated mutations. Most of the 40 new mutants exhibited phenotypes that resulted from eIF-5A protein-folding defects. Our data provided evidence that the C-terminal alpha-helix present in yeast eIF5A is an essential structural element, whereas the eIF5A N-terminal 10 amino acid extension not present in archaeal eIF5A homologs, is not. Moreover, the mutants containing substitutions at or in the vicinity of the hypusine modification site displayed nonviable or temperature-sensitive phenotypes and were defective in hypusine modification. Interestingly, two of the temperature-sensitive strains produced stable mutant eIF5A proteins--eIF5A(K56A) and eIF5A(Q22H,L93F)--and showed defects in protein synthesis at the restrictive temperature. Our data revealed important structural features of eIF5A that are required for its vital role in cell viability and underscored an essential function of eIF5A in the translation step of gene expression.     

Devoted fathers or selfish lovers? Conflict between mating effort and parental care in a harem‐defending arachnid

When there is a temporal trade‐off between mating effort and parental care, theoretical models predict that intense sexual selection on males leads to reduced paternal care. Thus, high‐quality males should invest more in mating effort because they have higher chances of acquiring mates, whereas low‐quality males should bias their investment towards parental care. Once paternal care has evolved, offspring value should also influence males’ decisions to invest in offspring attendance. Here, we performed a manipulation under field conditions to investigate the factors that influence male allocation in either mating effort or parental care. We predicted that facultative paternal care in the harem‐holding harvestman Serracutisoma proximum would be negatively influenced by male attractiveness and positively influenced by offspring value. We found that attractive males were less likely to engage in egg attendance and that the higher the perceived paternity, the higher the caring frequency. Finally, egg mortality was not related to caring frequency by males, but predation pressure was much lower than that recorded in previous studies with the same population. Thus, the benefits of facultative male care may be conditional to temporal variation in the intensity of egg predation. In conclusion, males adjust their investment in either territory defence or egg attendance according to their recent mating history and perceived paternity. Our findings suggest that exclusive paternal care can evolve from facultative paternal care only if the trade‐off between mating effort and parental care is circumvented.     

Pharmacological modulation of reactive oxygen species (ROS) improves the airway hyperresponsiveness by shifting the Th1 response in allergic inflammation induced by ovalbumin

Asthma is an allergic inflammation driven by the Th2 immune response with release of cytokines such as IL-4 and IL-13, which contribute to the airflow limitations and airway hyperresponsiveness (AHR). The involvement of oxidative stress in this process is well-established, but the specific role of the superoxide anion and nitric oxide in asthma are poorly understood. Thus, the aim of this study was to investigate the mechanisms underlying the superoxide anion/nitric oxide production and detoxification in a murine asthma model. BALB/c male mice were sensitised and challenged with ovalbumin (OVA). Pretreatments with either apocynin (14?mg/kg) or allopurinol (25?mg/kg) (superoxide anion synthesis inhibitors), aminoguanidine (50?mg/kg) (nitric oxide synthesis inhibitor) or diethyldithiocarbamate (100?mg/kg) (superoxide dismutase inhibitor) were performed 1?h before the challenge. Our data showed that apocynin and allopurinol ameliorated AHR and reduced eosinophil peroxidase, as well as IL-4 and IL-13 levels. Apocynin also abrogated leukocyte peribronchiolar infiltrate and increased IL-1β secretion. Aminoguanidine preserved lung function and shifted the Th2 to the Th1 response with a reduction of IL-4 and IL-13 and increase in IL-1β production. Diethyldithiocarbamate prevented neither allergen-induced AHR nor eosinophil peroxidase (EPO) generation. All treatments protected against oxidative damage observed by a reduction in TBARS levels. Taken together, these results suggest that AHR in an asthma model can be avoided by the down-regulation of superoxide anion and nitric oxide synthesis in a mechanism that is independent of a redox response. This down-regulation is also associated with a transition in the typical immunological Th2 response toward the Th1 profile.     

Ricochet pollination in Senna (Fabaceae) – petals deflect pollen jets and promote division of labour among flower structures

• Naturalists Fritz and Hermann Müller hypothesised that heteranthery often leads to a division of labour into ‘feeding’ and ‘pollinating’ stamens; the latter often being as long as the pistil so as to promote successful pollination on the bees’ back. In many buzz‐pollinated species of Senna, however, the so‐called pollinating stamens are short and not level with the stigma, raising the question of how pollen is shed on the bees’ back. Here we explore a mechanism called ‘ricochet pollination’. We test whether division of labour is achieved through the interaction between short lower stamens and strongly concave ‘deflector petals’.
• We studied the arrangement and morphology of the floral organs involved in the ricochet pollination, functioning of the flowers through artificial sonication and observed the interactions between bees and flowers in the field.
• The middle stamens are adapted to eject pollen downwards, which can be readily collected on the bee mid legs. Most of the pollen is ejected towards the deflector petal(s). Pollen from this set of stamens is more likely to contribute to pollination. The pollen grains seem to ricochet multiple times against the deflector petals to eventually reach the bee's back.
• The pollen ricochet mechanism promotes a division of labour by involving additional floral organs, such as petals, reinforcing the Müllers’ division‐of‐labour hypothesis. However, alternative, non‐multiexclusive hypotheses could be explored in genus Senna and other angiosperm species.

     

Alkaline cooking and tortilla quality in maize grains from the humid,tropical lands of Mexico

Maize (Zea mays L.) tortilla is the major staple food for the Mexican population. Nine tropical maize genotypes were evaluated. All samples had white grains, a common characteristic in tropical maize, and therefore they were appropriate for nixtamalized flour industry. Grain, flour, masa and tortilla characteristics of each maize genotype were evaluated. Length, width, thickness, weight of 1000 grains and hardness of grain were determined. Moisture content, proteins, fat, ash, mean particle size, water absorption index, enthalpy, and flour temperature were also evaluated. Adhesiveness and cohesiveness were evaluated in masa. Moisture content, protein, capacity to puff up, roll making, tension and cutting strength were determined in tortillas. There were significant differences (p≤0.05) in most of the evaluated characteristics. Grain length values varied between 9.26 and 11.02 mm for populations 23 and 22, respectively. Grain hardness oscillated between 11.17 (population 32) and 14.75 (landrace Mejen). According to the weight of 1000 grains most genotypes had small grains. The minimum and maximum moisture values of flour and tortillas were 8.33-9.99% and 46.20-50.36%, respectively. The texture of tortillas elaborated from population 32 and landrace Mejen had the lowest tension and cutting strength, resulting the best genotypes for making tortilla.     

Adhesion, growth and detachment of cells on modified polystyrene surface

By adsorbing poly(N-isopropylacrylamide) (PNIPAAm) from an aqueous solution onto oxidised polystyrene without the need for grafting the polymer to the surface, we showed here that cells(CHO-K1) adhere and grow well at 37 °C and are detached by lowering the temperature to 10 °C without any other deleterious treatment. Both bacterial culture grade polystyrene Petri dishes and polystyrene beads (120 to 250μm diameters) commercially available used in static conditions of growth were tested with similar results. The contact angle of modified Petri dishes with a water droplet increases from 36 to 58° when the temperature is raised from 25 to 37 °C indicating change in hydrophilicity of the surface as a function of temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Detection of responsible mutations for beta thalassemia in the Kermanshah Province of Iran using PCR-based techniques

Beta Thalassemia has been reported to be a common genetic disorder in Iran. To establish the molecular spectrum of the beta thalassemias in the Kermanshah Province of Iran, 185 unrelated beta thalassemia patients with Kurdish ethnic background were studied (181 β-thalassemia major and 4 β-thalassemia intermedia). Using polymerase chain reaction-amplification refractory mutation system (PCR-ARMS), restriction fragment length polymorphism (RFLP) and direct genomic sequencing twenty different mutations were identified accounting for 98.1% of the alleles. Approximately 80.8% of β-thalassemia chromosomes had β⁰ mutation. The most prevalent mutation was the IVSII-1 (G→A) (32.97%), followed by CD8/9 +G (13.51%), IVSI-110 (C→T) (8.38%), CD 36/37 −T (7.84%), CD8 −AA (5.94%), CD15 (G→A) (4.86%) and IVSI-1 (G→A) (4.59%). All of these mutations accounted for 78.1% of the alleles. The results described here will be of valuable help in the development of successful prevention programs for the population of Kermanshah.     

The phylogenetic potential of entire 26S rDNA sequences in plants

18S ribosomal RNA genes are the most widely used nuclear sequences for phylogeny reconstruction at higher taxonomic levels in plants. However, due to a conservative rate of evolution, 18S rDNA alone sometimes provides too few phylogenetically informative characters to resolve relationships adequately. Previous studies using partial sequences have suggested the potential of 26S or large-subunit (LSU) rDNA for phylogeny retrieval at taxonomic levels comparable to those investigated with 18S rDNA. Here we explore the patterns of molecular evolution of entire 26S rDNA sequences and their impact on phylogeny retrieval. We present a protocol for PCR amplification and sequencing of entire (approximately 3.4 kb) 26S rDNA sequences as single amplicons, as well as primers that can be used for amplification and sequencing. These primers proved useful in angiosperms and Gnetales and likely have broader applicability. With these protocols and primers, entire 26S rDNA sequences were generated for a diverse array of 15 seed plants, including basal eudicots, monocots, and higher eudicots, plus two representatives of Gnetales. Comparisons of sequence dissimilarity indicate that expansion segments (or divergence domains) evolve 6.4 to 10.2 times as fast as conserved core regions of 26S rDNA sequences in plants. Additional comparisons indicate that 26S rDNA evolves 1.6 to 2.2 times as fast as and provides 3.3 times as many phylogenetically informative characters as 18S rDNA; compared to the chloroplast gene rbcL, 26S rDNA evolves at 0.44 to 1.0 times its rate and provides 2.0 times as many phylogenetically informative characters. Expansion segment sequences analyzed here evolve 1.2 to 3.0 times faster than rbcL, providing 1.5 times the number of informative characters. Plant expansion segments have a pattern of evolution distinct from that found in animals, exhibiting less cryptic sequence simplicity, a lower frequency of insertion and deletion, and greater phylogenetic potential.      

Bacterial species and evolution: Theoretical and practical perspectives

A discussion of the species problem in modern evolutionary biology serves as the point of departure for an exploration of how the basic science aspects of this problem relate to efforts to map bacterial diversity for practical pursuits—for prospecting among the bacteria for useful genes and gene-products. Out of a confusing array of species concepts, the Cohesion Species Concept seems the most appropriate and useful for analyzing bacterial diversity. Techniques of allozyme analysis and DNA fingerprinting can be used to put this concept into practice to map bacterial genetic diversity, though the concept requires minor modification to encompass cases of complete asexuality. Examples from studies of phenetically definedBacillus species provide very partial maps of genetic population structure. A major conclusion is that such maps frequently reveal deep genetic subdivision within the phenetically defined specles; divisions that in some cases are clearly distinct genetic species. Knowledge of such subdivisions is bound to make prospecting within bacterial diversity more effective. Under the general concept of genetic cohesion a hypothetical framework for thinking about the full range of species conditions that might exist among bacteria is developed and the consequences of each such model for species delineation, and species identification are discussed. Modes of bacterial evolution, and a theory of bacterial speciation with and without genetic recombination, are examined. The essay concludes with thoughts about prospects for very extensive mapping of bacterial diversity in the service of future efforts to find useful products. In this context, evolutionary biology becomes the handmaiden of important industrial activities. A few examples of past success in commercializing bacterial gene-products from species ofBacillus and a few other bacteria are reviewed.