High-performance liquid chromatographic method for determination of the metabolism of polyunsaturated molecular species of phosphatidylserine labeled in the polar group

A reversed-phase HPLC method to monitor the incorporation of radiolabeled precursors into the polar group of individual polyunsaturated molecular species of phosphatidylserine (PS) is presented. PS labeled in the polar group was decarboxylated and subsequently converted to trinitrophenyl-phosphatidylethanolamine (Tnp-PE), which was separated into its molecular species by reversed-phase HPLC within 90 min, using a gradient of acetonitrile—methanol and ammonium acetate. A major feature of the method is the complete resolution of the stearoyl species, 18:0/20:4 and 18:0/22:6, at ambient temperature. By determining the amount of radioactivity incorporated into each fraction, the metabolism of individual molecular species of PS, and also of PE, labeled in the polar group can be investigated.     

Potent inhibition of the aortic smooth muscle maxi-K channel by clinical doses of ethanol

We investigated the effects ofclinically relevant ethanol concentrations (5-20 mM) on thesingle-channel kinetics of bovine aortic smooth muscle maxi-K channelsreconstituted in lipid bilayers (1:1palmitoyl-oleoyl-phosphatidylethanolamine:palmitoyl-oleoyl-phosphatidylcholine). Ethanol at 10 and 20 mMdecreased the channel open probability (P_o) by75 ± 20.3% mainly by increasing the mean closed time (+82 to+960%, n = 7). In some instances, ethanol alsodecreased the mean open time (40.8 ± 22.5%). TheP_o-voltage relation in the presence of 20 mMethanol exhibited a rightward shift in the midpoint of voltageactivation (V_1/2  17 mV), a slightlysteeper relationship (change in slope factor, k,  2.5 mV), and a decreased maximum P_o (from~0.82 to ~0.47). Interestingly, channels inhibited by ethanol atlow Ca²⁺ concentrations (2.5 µM) were veryresistant to ethanol in the presence of increased Ca²⁺ ( 20 µM). Alcohol consumption in clinically relevant amounts may alterthe contribution of maxi-K channels to the regulation of arterial tone.

     

Oxygenated CdS Buffer Layers Enabling High Open‐Circuit Voltages in Earth‐Abundant Cu2BaSnS4 Thin‐Film Solar Cells

Earth‐abundant Cu₂BaSnS₄ (CBTS) thin films exhibit a wide bandgap of 2.04–2.07 eV, a high absorption coefficient > 10⁴ cm^?1, and a p‐type conductivity, suitable as a top‐cell absorber in tandem solar cell devices. In this work, sputtered oxygenated CdS (CdS:O) buffer layers are demonstrated to create a good p–n diode with CBTS and enable high open‐circuit voltages of 0.9–1.1 V by minimizing interface recombination. The best power conversion efficiency of 2.03% is reached under AM 1.5G illumination based on the configuration of fluorine‐doped SnO₂ (back contact)/CBTS/CdS:O/CdS/ZnO/aluminum‐doped ZnO (front contact).     

Kinesin-related KIP3 of Saccharomyces cerevisiae Is Required for a Distinct Step in Nuclear Migration

Spindle orientation and nuclear migration are crucial events in cell growth and differentiation of many eukaryotes. Here we show that KIP3, the sixth and final kinesin-related gene in Saccharomyces cerevisiae, is required for migration of the nucleus to the bud site in preparation for mitosis. The position of the nucleus in the cell and the orientation of the mitotic spindle was examined by microscopy of fixed cells and by time-lapse microscopy of individual live cells. Mutations in KIP3 and in the dynein heavy chain gene defined two distinct phases of nuclear migration: a KIP3-dependent movement of the nucleus toward the incipient bud site and a dynein-dependent translocation of the nucleus through the bud neck during anaphase. Loss of KIP3 function disrupts the unidirectional movement of the nucleus toward the bud and mitotic spindle orientation, causing large oscillations in nuclear position. The oscillatory motions sometimes brought the nucleus in close proximity to the bud neck, possibly accounting for the viability of a kip3 null mutant. The kip3 null mutant exhibits normal translocation of the nucleus through the neck and normal spindle pole separation kinetics during anaphase. Simultaneous loss of KIP3 and kinesin-related KAR3 function, or of KIP3 and dynein function, is lethal but does not block any additional detectable movement. This suggests that the lethality is due to the combination of sequential and possibly overlapping defects. Epitope-tagged Kip3p localizes to astral and central spindle microtubules and is also present throughout the cytoplasm and nucleus.     

In vitro selections with RNAs of variable length converge on a robust catalytic core

In vitro selection is a powerful tool that can be used to understand basic principles of molecular evolution. We used in vitro selection to understand how changes in length and the accumulation of point mutations enable the evolution of functional RNAs. Using RNA populations of various lengths, we performed a series of in vitro experiments to select for ribozymes with RNA ligase activity. We identified a core ribozyme structure that was robust to changes in RNA length, high levels of mutagenesis, and increased selection pressure. Elaboration on this core structure resulted in improved activity which we show is consistent with a larger trend among functional RNAs in which increasing motif size can lead to an exponential improvement in fitness. We conclude that elaboration on conserved core structures is a preferred mechanism in RNA evolution. This conclusion, drawn from selections of RNAs from random sequences, is consistent with proposed evolutionary histories of specific biological RNAs. More generally, our results indicate that modern RNA structures can be used to infer ancestral structures. Our observations also suggest a mechanism by which structural outcomes of early RNA evolution would be largely reproducible even though RNA fitness landscapes consist of disconnected clusters of functional sequences.     

Spatial correlations of Diceroprocta apache and its host plants: evidence for a negative impact from Tamarix invasion

Abstract 1. The hypothesis that the habitat‐scale spatial distribution of the Apache cicada Diceroprocta apache Davis is unaffected by the presence of the invasive exotic saltcedar Tamarix ramosissima was tested using data from 205 1‐m² quadrats placed within the flood‐plain of the Bill Williams River, Arizona, U.S.A. Spatial dependencies within and between cicada density and habitat variables were estimated using Moran's I and its bivariate analogue to discern patterns and associations at spatial scales from 1 to 30 m. 2. Apache cicadas were spatially aggregated in high‐density clusters averaging 3 m in diameter. A positive association between cicada density, estimated by exuvial density, and the per cent canopy cover of a native tree, Goodding's willow Salix gooddingii, was detected in a non‐spatial correlation analysis. No non‐spatial association between cicada density and saltcedar canopy cover was detected. 3. Tests for spatial cross‐correlation using the bivariate I_YZ indicated the presence of a broad‐scale negative association between cicada density and saltcedar canopy cover. This result suggests that large continuous stands of saltcedar are associated with reduced cicada density. In contrast, positive associations detected at spatial scales larger than individual quadrats suggested a spill‐over of high cicada density from areas featuring Goodding's willow canopy into surrounding saltcedar monoculture. 4. Taken together and considered in light of the Apache cicada's polyphagous habits, the observed spatial patterns suggest that broad‐scale factors such as canopy heterogeneity affect cicada habitat use more than host plant selection. This has implications for management of lower Colorado River riparian woodlands to promote cicada presence and density through maintenance or creation of stands of native trees as well as manipulation of the characteristically dense and homogeneous saltcedar canopies.