Brownian motion in a non-homogeneous force field and photonic force microscope

The Photonic Force Microscope (PFM) is an opto-mechanical technique based on an optical trap that can be assumed to probe forces in microscopic systems. This technique has been used to measure forces in the range of pico- and femto-Newton, assessing the mechanical properties of biomolecules as well as of other microscopic systems. For a correct use of the PFM, the force field to measure has to be invariable (homogeneous) on the scale of the Brownian motion of the trapped probe. This condition implicates that the force field must be conservative, excluding the possibility of a rotational component. However, there are cases where these assumptions are not fulfilled Here, we show how to improve the PFM technique in order to be able to deal with these cases. We introduce the theory of this enhanced PFM and we propose a concrete analysis workflow to reconstruct the force field from the experimental time-series of the probe position. Furthermore, we experimentally verify some particularly important cases, namely the case of a conservative or rotational force-field

Feasibility of a V-Shaped Magnet Rotor to Convert Vibration into Rotation

Majority of the reported kinetic energy harvesting mechanisms involve translatory transduction mechanisms, which diverges from the long established rotary design for electromagnetic generators. A rotary design can offer a much smaller magnet-coil air gap and clearance guidance that translatory transducers simply cannot physically attain. Therefore, this research investigates the feasibility of implementing a V-shaped magnet rotor for the purpose of coupling base point excitation into rotation, which can eventually be coupled to a generator motor. It was also previously theorised that the nonlinear magnetic coupling can give rise to broadband nonlinear resonant behaviour. The resultant device aims to enhance the overall power conversion efficiency of the captured vibration energy

Genetic transformatin of potato with a triple R gene construct to confer resistance to late blight.

The cultivated potato, Solanum tuberosum is affected by a variety of diseases with late blight (LB) caused by Phytophthora infestans being the most severe. The disease is mostly controlled by the application of large quantities of fungicides, which represent a financial burden on farmers indeveloping countries and pose risks to both human health and the environment. A more effective and environmentally friendly strategy to prevent damages caused by P. infestans is to use resistant potato cultivars. In the early days of breeding for LB resistance, a small number of resistance (R) genes from the wild Mexican species, Solanum demissum, were introgressed into modern potato varieties. These genes conferred race-specific resistance, which was rapidly overcome by new isolates of the pathogen. Recently, a number of new R genes have been identified and cloned from several wild potato species .Taking advantage of genetic engineering, our strategy is to use three of these new R genes (RB, Rpiblb2 and Rpi-vnt1.1) in a triple gene construct, p CIP 99, based on the hypothesis that simultaneous mutation for pathogenicity against all three genes is unlikely, and therefore the resistance conferred by the construct should be durable. We plan to deploy the three stacked R genes into the potato variety “Victoria” (known in Kenya and Uganda as “Asante”). To date, we have produced more than 100 transgenic events which are currently being characterized. The pathogen population will be characterized concurrently to assess the expected durability of this resistance

Genetic characterization of HIV-1 subtype G envelope sequences by single genome analysis

Subtype G is the sixth most prevalent subtype of HIV-1 and is responsible for an estimated 1,500,000 infections worldwide. Although systematic analyses of a wide range of HIV-1 envelope sequences and neutralization have been performed, subtype G viruses are severely underrepresented in these studies. There is thus an important need to study subtype G envelope sequences and their neutralization capacities

Nuclear Export of the Oncoprotein v-ErbA Is Mediated by Acquisition of a Viral Nuclear Export Sequence

v-ErbA, an oncogenic derivative of the thyroid hormone receptor α (TRα) carried by the avian erythroblastosis virus, contains several alterations including fusion of a portion of avian erythroblastosis virus Gag to its N terminus, N- and C-terminal deletions, and 13 amino acid substitutions. Nuclear export of v-ErbA occurs through a CRM1-mediated pathway. In contrast, nuclear export of TRα and another isoform, TRβ, is CRM1-independent. To determine which amino acid changes in v-ErbA confer CRM1-dependent nuclear export, we expressed a panel of green and yellow fluorescent protein-tagged mutant and chimeric proteins in mammalian cells. The sensitivity of subcellular trafficking of these mutants to leptomycin B (LMB), a specific inhibitor of CRM1, was assessed by fluorescence microscopy. Our data showed that a nuclear export sequence resides within a 70-amino acid domain in the C-terminal portion of the p10 region of Gag, and in vitro binding assays demonstrated that Gag interacts directly with CRM1. However, a panel of ligand-binding domain mutants of v-ErbA lacking the Gag sequence exhibited greater nuclear localization in the presence of LMB, suggesting that the various amino acid substitutions/deletions may cause a conformation shift, unmasking an additional CRM1-dependent nuclear export sequence. In contrast, the altered DNA-binding domain of the oncoprotein did not contribute to CRM1-dependent nuclear export. Heterokaryon experiments revealed that v-ErbA did not undergo nucleocytoplasmic shuttling when the CRM1 export pathway was blocked by LMB treatment, suggesting that the ability to follow the export pathway used by TRα has been lost by the oncoprotein during its evolution. Our findings thus point to the intriguing possibility that acquisition of altered nuclear export capabilities contributes to the oncogenic properties of v-ErbA

Rapid genetic transformation of sweetpotato (Ipomoea batatas (L.) Lam) via organogenesis

An efficient and rapid Agrobacterium-mediated transformation method based on de novo (via callus) organogenesis has been developed from petioles with leaf for sweetpotato (Ipomoea batatas (L.) Lam). Stable transgenic sweetpotato plants cv. Jewel were obtained in six to ten weeks after infection with Agrobacterium tumefaciens hyper-virulent strain EHA105 harboring a binary vector pCIP45 bearing the nptII gene conferring resistance to kanamycin and a gene of interest. PCR and Southern analyses confirmed stable integration of both genes into the sweetpotato genome. The expression of the nptII gene was assessed by reverse-transcribed PCR and callus development in a high kanamycin medium. A two-step organogenesis regeneration using media containing 4-fluorophenoxyacetic acid (4-FA) and zeatin was used in two independent transformation experiments yielding 20% and 10% transformation efficiency, respectively. When using indolacetic acid (IAA) in regeneration media, the transformation efficiency dropped to 4.0%. It indicated an auxin to cytokinin treatment could improve the regeneration of transgenic calluses. This rapid organogenesis-based transformation strategy represents an important improvement over existing methods and will facilitate producing large-scale transgenic sweetpotato plants the genetic improvement of a crop that is reputed to be difficult to transform