Oligomeric properties and signal peptide binding by Escherichia coli Tat protein transport complexes

The Escherichia coli Tat apparatus is a protein translocation system that serves to export folded proteins across the inner membrane. The integral membrane proteins TatA, TatB and TatC are essential components of this pathway. Substrate proteins are directed to the Tat apparatus by specialized N-terminal signal peptides bearing a consensus twin-arginine sequence motif. Here we have systematically examined the Tat complexes that can be purified from overproducing strains. Our data suggest that the TatA, TatB and TatC proteins are found in at least two major types of high molecular mass complex in detergent solution, one consisting predominantly of TatA but with a small quantity of TatB, and the other based on a TatBC unit but also containing some TatA protein. The latter complex is shown to be capable of binding a Tat signal peptide. Using an alternative purification strategy we show that it is possible to isolate a TatABC complex containing a high molar excess of the TatA component.     

DNA analyses reveal abundant homoplasy in taxonomically important morphological characters of Eusiroidea (Crustacea,Amphipoda)

Eusiroidea is one of the 20 amphipod superfamilies that were erected to subdivide the very large and controversial suborder Gammaridea. Yet, the definition of the superfamily is not based on synapomorphies, but on a combination of diagnostic phenetic similarities that hold more or less consistently across families. Moreover, many of the characters used to define eusiroid families are suspected to show convergent evolution. The current classification of the Eusiroidea may therefore not reflect evolutionary relationships accurately. Here, we present a molecular phylogenetic re‐analysis of the Eusiroidea based on a comparison of 18S and 28S rDNA sequences of 73 species, representing 47 genera and 16 families that potentially belong to the superfamily. The results suggest that at least species belonging to 14 of these traditional families would be part of a eusiroid clade, increasing by more than twofold the species and generic richness of the group. However, most of the eusiroid families surveyed do not appear monophyletic. Finally, the analyses show that several important morphological characteristics, traditionally used in eusiroid taxonomy, are homoplastic.     

Diurnal variations in ventilatory and cardiorespiratory responses to submaximal treadmill exercise in females

Diurnal variations in ventilatory and cardiorespiratory responses to submaximal treadmill exercise were analysed in 11 eumenorrhoeic women and in 10 women using monophasic oral contraceptives. Subjects performed submaximal treadmill exercise at three intensities averaging 7, 8, and 9 km x h(-1), each for 4 min at 0800, 1300 and 1700 hours, assigned randomly on 3 separate days. Rectal temperature was measured before (T(rec(b))) and after (T(rec(a))) exercise. Cardiac frequency (f(c)), ventilation (V(E)), oxygen uptake (VO(2)), carbon dioxide output (VCO(2)), and respiratory exchange ratio (R) were assessed in the last minute of each stage of the exercise. Both T(rec(b)) and T(rec(a)) increased from 0800 to 1700 hours (P < 0.001). For a given submaximal work rate, VO(2) and VCO(2) were higher in the afternoon compared to the morning. Similarly, R was increased at 1700 hours compared to 0800 hours during the recovery period following exercise (P < 0.05). However, V(E) did not vary significantly during the day at any of the running intensities. No significant interactions (group x time of day) were observed in any of the studied parameters. In contrast to ventilation, the VO(2) and VCO(2) of the females during submaximal exercise were both affected by the time of day, without any differences between eumenorrhoeic women and users of oral contraceptives.     

An information-theoretic analysis of genetics, gender and age in cancer patients

Germline genetics, gender and hormonal-signaling pathways are all well described modifiers of cancer risk and progression. Although an improved understanding of how germline genetic variants interact with other cancer risk factors may allow better prevention and treatment of human cancer, measuring and quantifying these interactions is challenging. In other areas of research, Information Theory has been used to quantitatively describe similar multivariate interactions. We implemented a novel information-theoretic analysis to measure the joint effect of a high frequency germline genetic variant of the p53 tumor suppressor pathway (MDM2 SNP309 T/G) and gender on clinical cancer phenotypes. This analysis quantitatively describes synergistic interactions among gender, the MDM2 SNP309 locus, and the age of onset of tumorigenesis in p53 mutation carriers. These results offer a molecular and genetic basis for the observed sexual dimorphism of cancer risk in p53 mutation carriers and a model is proposed that suggests a novel cancer prevention strategy for p53 mutation carriers.     

Irreversible inhibition of aldolase by a phosphorylated alpha-dicarbonyl compound

The preparation of a phosphorylated alpha-dicarbonyl compound designed to specifically react with arginine residues of enzymes accepting phosphorylated compounds as effectors is reported, and shown to inhibit rabbit muscle aldolase in a time-dependent and irreversible manner. This irreversible inhibition occured in a buffer devoid of borate ions, suggesting that the presence of the phosphate moiety contributes in the stabilization of the adduct formed with arginine residues. Under the same conditions, the metalloenzyme iron superoxide dismutase, in which an arginine is known to be critical for the catalytic function, is not significantly inhibited.     

Characterization and amino acid sequence of IRT-4, a novel TEM-type enzyme with a decreased susceptibility to β-lactamase inhibitors

Abstract A novel procedure was used to purify a cytosolic chitinase from Candida albicans to electrophoretic homogeneity. The results represent the first demonstration of the purification of a fungal intracellular chitinase using the criterion of a single band detected following silver-staining of a polyacrylamide gel run under denaturing conditions. Purified chitinase had pH and temperature optima of 5.0 and 50°C, respectively. Inhibition of enzyme activity by allosamidin was pH-dependent occuring maximally at pH 8.0. Phospholipids had similar marked and highly specific effects on the activities of both the purified soluble enzyme and a solubilized microsomal chitinase from C. albicans . Evidence is provided for the existence of a complex chitinolytic system in this organism.     

An assessment of the AFLP method for investigating population structure in the red alga Chondrus crispus Stackhouse (Gigartinales, Florideophyceae)

The appropriateness of the Amplified Fragment Length Polymorphism (AFLP) technique for investigating Chondrus crispus Stackhouse populations in the Maritime Provinces of Canada was assessed. The AFLP procedure was first subjected to reproducibility testing and three shortcomings were noted: 1) failure to reproduce band intensity between replicate runs for the same individual and primer pair; 2) failure of some bands to replicate; 3) lack of reproducibility for complete replicate runs for some individuals and primer pairs. In the last-mentioned case, the lack of reproducibility resulted in characteristic electropherograms indicative of weak reactions. These weak runs can be attributed to poor restriction digest/ligation reactions and/or substandard PCR, these failures ultimately resulting from low and inconsistent DNA quality. We recommend that reproducibility testing should be completed routinely in studies using the AFLP technique. In the current work, only fragments and individuals that gave reproducible results were used in subsequent analyses. The AFLP method resulted in highly variable markers within and between the populations of C. crispus included in this investigation, which prevented successful resolution of population structure. This situation could result from a lack of suitability for AFLP markers in population genetic studies, and/or too extensive genetic variation for C. crispus populations to be discerned by the AFLP technique. These two possible explanations are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

E-Readers and Visual Fatigue

The mass digitization of books is changing the way information is created, disseminated and displayed. Electronic book readers (e-readers) generally refer to two main display technologies: the electronic ink (E-ink) and the liquid crystal display (LCD). Both technologies have advantages and disadvantages, but the question whether one or the other triggers less visual fatigue is still open. The aim of the present research was to study the effects of the display technology on visual fatigue. To this end, participants performed a longitudinal study in which two last generation e-readers (LCD, E-ink) and paper book were tested in three different prolonged reading sessions separated by - on average - ten days. Results from both objective (Blinks per second) and subjective (Visual Fatigue Scale) measures suggested that reading on the LCD (Kindle Fire HD) triggers higher visual fatigue with respect to both the E-ink (Kindle Paperwhite) and the paper book. The absence of differences between E-ink and paper suggests that, concerning visual fatigue, the E-ink is indeed very similar to the paper.