Thermal conductivity and dielectric constant of silicate materials

Report on the thermal conductivity and dielectric constant of nonmetallic materials evaluates the mechanisms of heat transfer in evacuated silicate powders and establishes the complex dielectric constant of these materials. Experimental measurements and results are related to postulated lunar surface materials

Interaction of the Xanthine Nucleotide Binding Goα Mutant with G Protein-coupled Receptors

We constructed a double mutant version of the α subunit of Go that was regulated by xanthine nucleotides instead of guanine nucleotides (GoαX). We investigated the interaction between GoαX and G protein-coupled receptors in vitro. First, we found that the activated m2 muscarinic cholinergic receptor (MAChR) could facilitate the exchange of XTPγS for XDP in the GoαXβγ heterotrimer. Second, the GoαXβγ complex was able to induce the high affinity ligand-binding state in the N-formyl peptide receptor (NFPR). These experiments demonstrated that GoαX was able to interact effectively with G protein-coupled receptors. Third, we found that the empty form of GoαX, lacking a bound nucleotide and βγ, formed a stable complex with the m2 muscarinic cholingeric receptor associated with the plasma membrane. Finally, we investigated the interaction of GoαX with receptor in COS-7 cells. The empty form of GoαX bound tightly to the receptor and was not activated because XTP was not available intracellularly. We tested the ability of GoαX to inhibit the activities of several different G protein-coupled receptors in transfected COS-7 cells and found that Goα X specifically inhibited Go-coupled receptors. Thus the modified G proteins may act as dominant-negative mutants to trap and inactivate specific subsets of receptors

Phase variation and the Hin protein: in vivo activity measurements, protein overproduction, and purification

The alternate expression of the Salmonella flagellin genes H1 and H2 is controlled by the orientation of a 995-base-pair invertible segment of DNA located at the 5' end of the H2 gene. The hin gene, which is encoded within the invertible region, is essential for the inversion of this DNA segment. We cloned the hin gene into Escherichia coli and placed it under the control of the PL promoter of bacteriophage lambda. These cells overproduced the Hin protein. In vivo inversion activity was measured by using a recombinant lambda phage which contains the H2 and lacZ genes under the control of the invertible region. Using this phage, we showed that the amount of inversion activity is proportional to the amount of Hin protein in the cell. An inactive form of the protein was purified by using the unusual solubility properties of the overproduced protein. The amino acid composition of the protein agreed with the DNA sequence of the hin gene. Antibodies were made to the isolated protein. These antibodies cross-reacted with two other unidentified E. coli proteins

The entry of diphtheria toxin into the mammalian cell cytoplasm: evidence for lysosomal involvement

Lysosomotropic amines, such as ammonium chloride, are known to protect cells from the cytotoxic effects of diphtheria toxin. These drugs are believed to inhibit the transport of the toxin from a receptor at the cell exterior into the cytoplasm where a fragment of the toxin arrests protein synthesis. We studied the effects of lysosomotropic agents on the cytotoxic process to better understand how the toxin enters the cytoplasm. The cytotoxic effects of diphtheria toxin were not inhibited by antitoxin when cells were preincubated at 37 degrees C with toxin and ammonium chloride, exposed to antitoxin at 4 degrees C, washed to relieve the ammonium chloride inhibition, and finally warmed to 37 degrees C. The antigenic determinants of the toxin were, therefore, either altered or sheltered. It is likely that the combination of ammonium chloride and a low temperature trapped the toxin in an intracellular vesicle from which the toxin could proceed to the cytoplasm. Because lysosomotropic amines raise the pH within acidic intracellular vesicles, such as lysosomes, they could trap the toxin within such a vesicle if an acidic environment were necessary for the toxin to penetrate into the cytoplasm. We simulated acidic conditions which the toxin might encounter by exposing cells with toxin bound to their surface to acidic medium. We then measured the effects of lysosomotropic amines on the activity of the toxin to see if the acidic environment substituted for the function normally inhibited by the drugs. The drugs no longer protected the cells. This suggests that exposing the toxin to an acidic environment, such as that found within lysosomes, is an important step in the penetration of diphtheria toxin into the cytoplasm

Archaeal ubiquity

In the seventeenth century, Antoine von Leeuwenhook used a simple microscope to discover that we live within a previously undetected microbial world containing an enormously diverse population of creatures. The late nineteenth and early twentieth century brought advances in microbial culture techniques and in biochemistry, uncovering the roles that microbes play in all aspects of our world, from causing disease to modulating geochemical cycles. In the last 25 years, molecular biology has revealed the complexity and pervasiveness of the microbial world and its importance for understanding the interactions that maintain living systems on the planet. The paper by Preston et al. (1) in this issue of the Proceedings provides a clear illustration of the power of these molecular techniques to describe new biological relationships and to pose important questions about the mechanisms that drive evolution. The analysis of ribosomal RNA gene sequences is one molecular approach that has radically altered our view of microbial diversity. Its application can be extended and expedited by the use of PCR. The confluence of these techniques has stimulated the rapid assembly of sequence information from homologues rRNA gene regions derived from virtually all classes of organisms. The data collected thus far support the scheme first presented by Woese et al. (2), which holds that the relationships among organisms can be summarized in the form of a universal phylogenetic tree comprised of one eukaryotic and two prokaryotic domains: the Eucarya, the Bacteria, and the Archaea (Fig. 1)

A strong law of large numbers for branching processes: almost sure spine events

We demonstrate a novel strong law of large numbers for branching processes, with a simple proof via measure-theoretic manipulations and spine theory. Roughly speaking, any sequence of events that eventually occurs almost surely for the spine entails the almost sure convergence of a certain sum over particles in the population.Comment: 6 page