Strong Constraints on Cosmological Gravity from GW170817 and GRB 170817A.

The detection of an electromagnetic counterpart (GRB 170817A) to the gravitational-wave signal (GW170817) from the merger of two neutron stars opens a completely new arena for testing theories of gravity. We show that this measurement allows us to place stringent constraints on general scalar-tensor and vector-tensor theories, while allowing us to place an independent bound on the graviton mass in bimetric theories of gravity. These constraints severely reduce the viable range of cosmological models that have been proposed as alternatives to general relativistic cosmology.

HrpZ(Psph) from the plant pathogen Pseudomonas syringae pv. phaseolicola binds to lipid bilayers and forms an ion-conducting pore in vitro.

The hrp gene clusters of plant pathogenic bacteria control pathogenicity on their host plants and ability to elicit the hypersensitive reaction in resistant plants. Some hrp gene products constitute elements of the type III secretion system, by which effector proteins are exported and delivered into plant cells. Here, we show that the hrpZ gene product from the bean halo-blight pathogen, Pseudomonas syringae pv. phaseolicola (HrpZ(Psph)), is secreted in an hrp-dependent manner in P. syringae pv. phaseolicola and exported by the type III secretion system in the mammalian pathogen Yersinia enterocolitica. HrpZ(Psph) was found to associate stably with liposomes and synthetic bilayer membranes. Under symmetric ionic conditions, addition of 2 nM of purified recombinant HrpZ(Psph) to the cis compartment of planar lipid bilayers provoked an ion current with a large unitary conductivity of 207 pS. HrpZ(Psph)-related proteins from P. syringae pv. tomato or syringae triggered ion currents similar to those stimulated by HrpZ(Psph). The HrpZ(Psph)-mediated ion-conducting pore was permeable for cations but did not mediate fluxes of Cl-. Such pore-forming activity may allow nutrient release and/or delivery of virulence factors during bacterial colonization of host plants.

Assembly of tropomyosin isoforms into the cytoskeleton of avian muscle cells.

Tropomyosin (TM) is a component of microfilaments of most eukaryotic cells. In striated muscle, TM helps confer calcium sensitivity to the actin-myosin interaction. TM is a fibrillar, self-associating protein that binds to the extended actin filament system. We hypothesized that these structural features would permit TM to undergo assembly into the cytoskeleton during translation, or cotranslational assembly. Pulse-chase experiments with [35S]methionine and pulse experiments with [3H]puromycin followed by extraction and immunoprecipitation of TM were performed to examine the mechanism of assembly of TM into the cytoskeleton in cultured avian muscle cells. Pulse-chase experiments provide kinetic evidence for cotranslational assembly of TM in skeletal and cardiac muscle. Demonstration of a large majority of completed TM on purified skeletal muscle microfilaments after a short labeling period confirms that these kinetic data are not related to trapping of TM within the actin network of the cytoskeleton. Nascent TM peptides are demonstrated on the cytoskeleton of muscle cells after a short metabolic pulse followed by puromycin treatment to release nascent peptides from ribosomes or after labeling with [3H]puromycin. Nascent chain localization to the cytoskeleton independent of ribosomal attachment further confirms the high degree of cotranslational assembly of this protein. The extent of cotranslational assembly is similar before and after the formation of significant myofibril in myotubes, suggesting that cotranslational assembly of TM is active during contractile apparatus assembly in muscle differentiation. This is the first report where assembly mechanism has been predicted to be cotranslational based upon structural features of a cytoskeletal protein.

Expression and characterization of a trpl homolog from rat.

Mammalian homologues of the Drosophila trp/trpl-gene-family code for "Ca(2+)-store-operated" channels. Here we describe the cloning and expression of a trp/trpl homologous gene from rat brain. The clone is named Rtrp3 because of its high homology to the recently described Htrp3 (Zhu et al (1996) Cell 85:661-671). Expression of Rtrp3 in the mammalian COS-1 cell line leads to 100% increase of capacitative Ca2+ entry as compared to the controls. This capacitative calcium entry can be completely blocked with La3+ (10 microM). We conclude that Rtrp3, a new member of the growing family of trp/trpl homologues in mammalians, is involved in "Ca(2+)-store-operated" Ca2+ entry into the cell.

An eye for evaluation.

A model is developed by which evaluation of social work services can study a cross-section of factors which affect the performance of that service. It demonstrates how the boundaries of an evaluation can be defined without developing a biased pattern of accountability.