First Limit on the Direct Detection of Lightly Ionizing Particles for Electric Charge as Low as e/1000 with the Majorana Demonstrator.

The Majorana Demonstrator is an ultralow-background experiment searching for neutrinoless double-beta decay in ^{76}Ge. The heavily shielded array of germanium detectors, placed nearly a mile underground at the Sanford Underground Research Facility in Lead, South Dakota, also allows searches for new exotic physics. Free, relativistic, lightly ionizing particles with an electrical charge less than e are forbidden by the standard model but predicted by some of its extensions. If such particles exist, they might be detected in the Majorana Demonstrator by searching for multiple-detector events with individual-detector energy depositions down to 1 keV. This search is background-free, and no candidate events have been found in 285 days of data taking. New direct-detection limits are set for the flux of lightly ionizing particles for charges as low as e/1000.

Search for Neutrinoless Double-ß Decay in

The Majorana Collaboration is operating an array of high purity Ge detectors to search for neutrinoless double-ß decay in ^{76}Ge. The Majorana Demonstrator comprises 44.1 kg of Ge detectors (29.7 kg enriched in ^{76}Ge) split between two modules contained in a low background shield at the Sanford Underground Research Facility in Lead, South Dakota. Here we present results from data taken during construction, commissioning, and the start of full operations. We achieve unprecedented energy resolution of 2.5 keV FWHM at Q_{ßß} and a very low background with no observed candidate events in 9.95 kg yr of enriched Ge exposure, resulting in a lower limit on the half-life of 1.9×10^{25} yr (90% C.L.). This result constrains the effective Majorana neutrino mass to below 240-520 meV, depending on the matrix elements used. In our experimental configuration with the lowest background, the background is 4.0_{-2.5}^{+3.1} counts/(FWHM t yr).

The potassium channel KcsA and its interaction with the lipid bilayer.

The crystal structure of the K+ channel KcsA explains many features of ion channel function. The selectivity filter corresponds to a narrow region about 12 Along and 3 A wide, lined by carbonyl groups of the peptide backbone, through which a K+ ion can only move ina dehydrated form. The selectivity filter opens into a central, water-filled cavity leading to a gating site on the intracellular side of the channel. The channel is tetrameric, each monomer containing two transmembrane a helices, M1 and M2. Helix M1 faces the lipid bi-layer and helix M2 faces the central channel pore; the M2 helices participate in subunit-subunit interactions. Helices M1 and M2 in each subunit pack as a pair of antiparallel coils with a heptad repeat, but the M2 helices of neighbouring subunits show fewer interactions, crossing at an angle of about -40 degrees. Trp residues at the ends of the transmembrane a helices form clear girdles on the two faces of the membrane, which, together with girdles of charged residues, define a hydrophobic thickness of about 37 A for the channel. Binding constants for phosphatidylcholines to KcsA vary with fatty acyl chain length, the optimum chain length being C22. A phosphatidylcholine with this chain length gives a bilayer of thickness about 34 A in the liquid crystalline phase, matching the hydrophobic thickness of the protein. However, a typical biological membrane has a hydrophobic thickness of about 27 A. Thus either the transmembrane a helices of KcsA are more tilted in the native membrane than they are in the crystal structure, or the channel is under stress in the native membrane. The efficiency of hydrophobic matching between KcsA and the surrounding lipid bilayer is high over the chain length range C10-C24. The channel requires the presence of some anionic lipids for function, and fluorescence quenching studies show the presence of two classes of lipid binding site on KcsA; at one class of site (nonannular sites) anionic phospholipids bind more strongly than phosphatidylcholine, whereas at the other class of site (annular sites) phosphatidylcholines and anionic phospholipids bind with equal affinity.

Drosophila yolk protein produced in E. coli is accumulated by mosquito ovaries.

Despite similar functions, the yolk proteins of the higher dipteran flies and the vitellogenins found in other insects are unrelated at the sequence level and have evolved from different genes. Both are selectively endocytosed into the ovary via receptors belonging to the LDLR receptor subfamily. We cloned the Drosophila yp1 gene into an E. coli expression vector and showed that the yolk protein produced by E. coli is taken up into ovaries of both Drosophila melanogaster and the malaria mosquito Anopheles gambiae, which normally uses vitellogenin.