Magneto-optical stokes polarimetry and nanostructured magnetic materials

Stokes parameters fully characterize the polarization state of light in an experimentally accessible manner. Photoelastic modulator (PEM) based Stokes polarimetry offers a very high sensitivity which is particularly suitable for the investigation of the magneto-optical properties of nanostructured magnetic materials. In this paper, we shall describe a robust methodology recently developed by us that utilizes a dual PEM setup. As an example of its application, we report on the magneto-optical characteristics of focused Ga ion beam patterned Fe films. We have investigated Ga ion irradiation of single-layer polycrystalline Fe films deposited on Si3N4 substrates, which allows us to study the effects of ion implantation with minimum added complications. Complemented by structural and other characterization techniques, the absolute measurement of magneto-optical effects through the determination of Stokes parameters has enabled us to effectively separate the various contributions from film thinning due to sputtering, structural modifications and compositional changes caused by Ga incorporation. A comparison is also made between the magneto-optical behavior of patterned thin films and that of anodic aluminum oxide embedded magnetic nanowire arrays.

The time-dependent structural and magnetic properties of CoPt nanowire arrays by AC electrodeposition

High areal density CoPt alloy nanowire arrays have been fabricated in anodic aluminum oxide templates by AC electrodeposition. We demonstrate that the AC electrodeposition time in this technique is a very important parameter for the microstructure and magnetic properties of the nanowire arrays. It is found that the mean length of the nanowire arrays, for given electrodeposition conditions, may reach a maximum value at a certain electrodeposition time. As nanowire arrays reach their maximum length, magnetic switching jump in hysteresis loops is observed and it becomes more remarkable with further increasing the deposition time. The corresponding origins of these properties are discussed.

Evaluation of polymerase chain reaction (PCR) method and hybrid capture II (HCII) assay for the detection of human papillomavirus in cervical scrapings

In order to investigate the reliability of detecting HPV DNA in cervical smears, we compared the performance of nested MY/GP PCR and FDA approved-Hybrid Capture II (HCII) using clinical cervical scrapings from 40 patients. It was found that PCR was more sensitive (81.8%) in comparison to HCII (36.4%) in detecting HPV although specificity of HCII was much higher (96.6%) than PCR (58.6%). The Negative Predictive Value (NPV) of both the techniques were quite similar but Positive Predictive Value (PPV) of HCII was much higher (80.0%) compared to PCR (42.9%). While the HCII method showed good specificity for HPV detection, its lack of sensitivity as compared to PCR may be a drawback for diagnostic use.

Identification of a putative effector protein for rab11 that participates in transferrin recycling

We have identified and cloned the cDNA for a 912-aa protein, rab11BP, that interacts with the GTP-containing active form of rab11, a GTP-binding protein that plays a critical role in receptor recycling. Although rab11BP is primarily cytosolic, a significant fraction colocalizes with rab11 in endosomal membranes of both the sorting and recycling subcompartments. In vitro binding of rab11 to native rab11BP requires partial denaturation of the latter to expose an internal binding site located between residues 334 and 504 that is apparently masked by the C-terminal portion of the protein, which includes six repeats known as WD40 domains. Within the cell, rab11BP must undergo a conformational change in which the rab11-binding site becomes exposed, because when coexpressed with rab11 in transfected cells the two proteins formed abundant complexes in association with membranes. Furthermore, although overexpression of rab11BP did not affect transferrin recycling, overexpression of a truncated form of the protein, rab11BP(1-504), that includes the rab11-binding site but lacks the WD40 domains inhibited recycling as strongly as does a dominant negative rab11 mutant protein that does not bind GTP. Strikingly, the inhibition caused by the truncated rab11BP was prevented completely when the cells also expressed a C-terminally deleted, nonprenylatable form of rab11 that, by itself, has no effect on recycling. We propose that rab11BP is an effector for rab11, whose association with this GTP-binding protein is dependent on the action of another membrane-associated factor that promotes the unmasking of the rab11-binding site in rab11BP.

Coatomer, but not P200/myosin II, is required for the in vitro formation of trans-Golgi network-derived vesicles containing the envelope glycoprotein of vesicular stomatitis virus

Using a cytosol and nucleotide dependent assay that we previously developed, we have investigated the requirement for coat proteins in the in vitro production of trans-Golgi network (TGN)-derived vesicles from a Madin-Darby canine kidney (MDCK) cell Golgi fraction that contains the 35S-labeled, terminally glycosylated, envelope glycoprotein of vesicular stomatitis virus (VSV-G) accumulated in the TGN. We found that the TGN-derived vesicles, like those involved in intra-Golgi transport and in retrograde transport to the endoplasmic reticulum, contain a coatomer coat and that coatomer is required for their formation. Thus, after they are produced with GTPgammaS, the coated vesicles could be captured on beads containing anticoatomer antibody. Moreover, a cytosolic protein fraction depleted of coatomer could not support vesicle formation but it did so after purified coatomer was added. We also determined that P200/myosin II does not play an essential role in the in vitro generation of TGN-derived vesicles. Thus, removal of this protein from the cytosol, by differential salt precipitation or binding to phalloidin-induced actin filaments, had no effect on vesicle generation. Nevertheless, immunodepletion of cytosol using the anti-P200/myosin II AD7 antibody abolished vesicle generation and that antibody was capable of effectively immunocapturing coated vesicles, even when these were generated in the absence of P200/myosin II. These effects, however, are explained by the unexpected finding that the AD7 antibody interacts with undenatured coatomer.