ALBERT

Description: Nature Physics 9, 636 (2013). doi:10.1038/nphys2743 Authors: F. K. Dejene, J. Flipse, G. E. W. Bauer & B. J. van Wees Since the discovery of the giant magnetoresistance effect the intrinsic angular momentum of the electron has opened up new spin-based device concepts. Our present understanding of the coupled transport of charge, spin and heat relies on the two-channel model for spin-up and spin-down electrons having equal temperatures. Here we report the observation of different (effective) temperatures for the spin-up and spin-down electrons in a nanopillar spin valve subject to a heat current. By three-dimensional finite element modelling of our devices for varying thickness of the non-magnetic layer, spin heat accumulations (the difference of the spin temperatures) of 120 mK and 350 mK are extracted at room temperature and 77 K, respectively, which is of the order of 10% of the total temperature bias over the nanopillar. This technique uniquely allows the study of inelastic spin scattering at low energies and elevated temperatures, which is not possible by spectroscopic methods.

Description: Background: Cotton is the world's primary fiber crop and is a major agricultural commodity in over 30 countries. Like many other global commodities, sustainable cotton production is challenged by restricted natural resources. In response to the anticipated increase of agricultural water demand, a major research direction involves developing crops that use less water or that use water more efficiently. In this study, our objective was to identify differentially expressed genes in response to water deficit stress in cotton. A global expression analysis using cDNA-Amplified Fragment Length Polymorphism was conducted to compare root and leaf gene expression profiles from a putative drought resistant cotton cultivar grown under water deficit stressed and well watered field conditions. Results: We identified a total of 519 differentially expressed transcript derived fragments. Of these, 147 transcript derived fragment sequences were functionally annotated according to their gene ontology. Nearly 70 percent of transcript derived fragments belonged to four major categories: 1) unclassified, 2) stress/defense, 3) metabolism, and 4) gene regulation. We found heat shock protein-related and reactive oxygen species-related transcript derived fragments to be among the major parts of functional pathways induced by water deficit stress. Also, twelve novel transcripts were identified as both water deficit responsive and cotton specific. A subset of differentially expressed transcript derived fragments was verified using reverse transcription-polymerase chain reaction. Differential expression analysis also identified five pairs of duplicated transcript derived fragments in which four pairs responded differentially between each of their two homologues under water deficit stress. Conclusions: In this study, we detected differentially expressed transcript derived fragments from water deficit stressed root and leaf tissues in tetraploid cotton and provided their gene ontology, functional/biological distribution, and possible roles of gene duplication. This discovery demonstrates complex mechanisms involved with polyploid cotton's transcriptome response to naturally occurring field water deficit stress. The genes identified in this study will provide candidate targets to manipulate the water use characteristics of cotton at the molecular level.

Description: 〈sec〉〈st〉Synopsis〈/st〉〈p〉〈textbox textbox-type="graphic"〉〈p〉〈inline-fig〉〈/inline-fig〉〈/p〉〈/textbox〉〈/p〉 〈p〉How AAA ATPases harness energy from ATP to promote directional translocation of polypeptides across membranes is poorly understood. Single-molecule FRET reveals that bacterial SecA uses ATP hydrolysis to push a polypeptide segment into the SecY channel, and phosphate release to slide it through the SecA-SecY complex.〈/p〉 〈p〉 〈l type="unord"〉〈li〉〈p〉SecA two-helix finger and clamp domains move upon ATP binding, hydrolysis and phosphate release.〈/p〉〈/li〉 〈li〉〈p〉ATP binding moves the two-helix finger towards the SecY channel, causing insertion of the first polypeptide segment into the channel.〈/p〉〈/li〉 〈li〉〈p〉Upon ATP hydrolysis, finger retraction and clamp domain closure around the translocating polypeptide ensure the translocation progress.〈/p〉〈/li〉 〈li〉〈p〉Clamp opening induced by phosphate release permits passive sliding of the polypeptide in either direction.〈/p〉〈/li〉〈/l〉 〈/p〉〈/sec〉

Description: 〈p〉SecA belongs to the large class of ATPases that use the energy of ATP hydrolysis to perform mechanical work resulting in protein translocation across membranes, protein degradation, and unfolding. SecA translocates polypeptides through the SecY membrane channel during protein secretion in bacteria, but how it achieves directed peptide movement is unclear. Here, we use single-molecule FRET to derive a model that couples ATP hydrolysis-dependent conformational changes of SecA with protein translocation. Upon ATP binding, the two-helix finger of SecA moves toward the SecY channel, pushing a segment of the polypeptide into the channel. The finger retracts during ATP hydrolysis, while the clamp domain of SecA tightens around the polypeptide, preserving progress of translocation. The clamp opens after phosphate release and allows passive sliding of the polypeptide chain through the SecA-SecY complex until the next ATP binding event. This power-stroke mechanism may be used by other ATPases that move polypeptides.〈/p〉