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B D Davis

Publications and source records attributed to B D Davis.

At least 55 records · Page 3Linked to original sources
PubMed1986

Misread protein creates membrane channels: an essential step in the bactericidal action of aminoglycosides.

Among the pleiotropic effects of aminoglycosides, their irreversible uptake and their blockade of initiating ribosomes have appeared to explain their bactericidal action, while the contributions of translational misreading and membrane damage and the mechanism of that damage have remained uncertain. We now present evidence that incorporation of misread proteins into the membrane can account for the membrane damage. The bactericidal action thus appears to result from the following sequence, in which each step is essential: slight initial entry of the antibiotic; interaction with chain-elongating ribosomes, resulting in misreading; incorporation of misread protein into the membrane, creating abnormal channels; increased (and irreversible) entry through these channels, and hence increased misreading and formation of channels; and, finally, blockade of initiating ribosomes. This mechanism can account for several previously unexplained observations: that streptomycin uptake requires protein synthesis during, but not after, the lag before the membrane damage; that streptomycin-resistant cells, which fail to take up streptomycin, can do so after treatment by another aminoglycoside; and that puromycin at moderate concentrations accelerates streptomycin uptake, while high concentrations (which release shorter chains) prevent it. In addition, puromycin, prematurely releasing polypeptides of normal sequence, also evidently creates channels, since it is reported to promote streptomycin uptake even in streptomycin-resistant cells. These findings imply that normal membrane proteins must be selected not only for a hydrophobic anchoring surface, but also for a tight fit in the membrane.

Alkaline Phosphatase↗
PubMed1986

Role of ribosome degradation in the death of starved Escherichia coli cells.

In Escherichia coli cultures limited for phosphate, the number of ribosomal particles was reduced to a small percentage of its earlier peak value by the time the viable cell count began to drop; the 30S subunits decreased more than the 50S subunits. Moreover, the ribosomal activity was reduced even more: these cells no longer synthesized protein, and their extracts could not translate phage RNA unless ribosomes were added. The translation initiation factors also disappeared, suggesting that they become less stable when released from their normal attachment to 30S subunits. In contrast, elongation factors, aminoacyl-tRNA synthetases, and tRNA persisted. During further incubation, until viability was reduced to 10(-5), the ribosomal particles disappeared altogether, while tRNA continued to be preserved. These results suggest that an excessive loss of ribosomes (and of initiation factors) may be a major cause of cell death during prolonged phosphate starvation.

Bacterial Proteins↗
PubMed1986

Hexachlorobenzene in hazardous waste sites.

Hexachlorobenzene (HCB) has been measured in the water, soil, air or biota at several uncontrolled hazardous waste sites. At one of these sites in Louisiana, 9,500,000 ppb have been measured in the oily fraction of an oil-water mixture taken from a monitoring well, and in water of nearby wells at concentrations up to 28 ppb. HCB has been detected in solid wastes and sediments at concentrations up to 6,000,000 ppb at a site in Michigan, while fish in a nearby creek contained up to 50 ppb. At other sites, HCB has been detected in air. Thus, exposure to this chemical may occur by several routes. Hazardous waste sites containing HCB, which are now being cleaned up under Superfund, include sites used for disposal of by-products of rubber manufacture, liquid-waste processing and incineration, and pesticide production. The variety of known sources of HCB suggests that its occurrence in hazardous waste sites may be widespread.

Animals↗
PubMed1985

Secretory S complex of Bacillus subtilis forms a large, organized structure when released from ribosomes.

The S complex of Bacillus subtilis, a set of four proteins that appears to be involved in protein secretion, is shown to be attached to 70S ribosomes: antibody to its 64-kDa component can aggregate these ribosomes, and the complex can be chemically crosslinked to ribosomal proteins. Low Mg2+ or prolonged high-speed centrifugation in a sucrose gradient releases the S complex from the ribosomes, and it is recovered as an aggregate with an S value of 76. Electron microscopy shows that these aggregates have a regular structure, somewhat resembling clathrin cages, with a diameter of about 45 nm. If these aggregates are physiological, their function would differ significantly from that of the signal recognition particle of eukaryotes.

Bacillus subtilis↗
PubMed1984

The 64-kilodalton membrane protein of Bacillus subtilis is also present as a multiprotein complex on membrane-free ribosomes.

The 64-kDa membrane protein of Bacillus subtilis is evidently involved in the attachment of secreting ribosomes to membrane. On immunoprecipitation with antibody to this protein, the solubilized particulate fraction, with or without prior chemical cross-linking, yields a complex of four proteins (64, 60, 41, and 36 kDa). This "S complex" was found to be associated with membrane-free ribosomes rather than with membrane, but the 64-kDa protein is also present, without the other proteins of the S complex, in the membrane-ribosome fraction and in the cytosol. Only the form present in the membrane-ribosome fraction is protected from protease. These findings suggest a cycle in which the complex participates in initiation of secretion but not in the later stages. It is not yet clear whether the 64-kDa protein found in the membrane-ribosome complexes is retained from the S complex after initiation and later recycled via the cytosol or whether it is a separate pool.

Bacillus subtilis↗
PubMed1984

Regulation of alpha-amylase activity in bean stem tissues.

alpha-Amylase activity was assayed in 1-centimeter sections taken from bean (Phaseolus vulgaris var. Kentucky Wonder) hypocotyls and epicotyls at measured distances from the cotyledons. The activity was low throughout the hypocotyl for the first 7 days. An increase was first observed with etiolated hypocotyls in the basal region, becoming higher in the more central regions by 14 to 17 days. By 21 days the activity was highest in the upper region, but had decreased in the lower regions. A comparable pattern was observed for the epicotyl from etiolated seedlings, the activity increasing first in the region closest to the cotyledons. These increases were associated with loss of cells from the pith in the hypocotyl and epicotyl of both dark- and light-grown plants. Since the changes were observed in tissues virtually devoid of starch, it is hypothesized that the control mechanism is related to the cellular disassembly associated with the mobilization of materials released during senescence rather than to a regulation by the enzyme's substrate or products.

Journal Article↗
PubMed1984

Energy-requiring translocation of the OmpA protein and alkaline phosphatase of Escherichia coli into inner membrane vesicles.

In developing a reliable in vitro system for translocating bacterial proteins, we found that the least dense subfraction of the membrane of Escherichia coli was superior to the total inner membrane, both for a secreted protein (alkaline phosphatase) and for an outer membrane protein (OmpA). Compounds that eliminated the proton motive force inhibited translocation, as already observed in cells; since protein synthesis continued, the energy for translocation appears to be derived from the energized membrane and not simply from ATP. Treatment of the vesicles with protease, under conditions that did not interfere with subsequent protein synthesis, also inactivated them for subsequent translocation. We conclude that export of some proteins requires protein-containing machinery in the cytoplasmic membrane that derives energy from the proton motive force.

Alkaline Phosphatase↗
PubMed1983

A 64-kilodalton membrane protein of Bacillus subtilis covered by secreting ribosomes.

The complexed (ribosome-bearing) membrane fraction of Bacillus subtilis contains several proteins (CM-proteins) that are virtually absent from the ribosome-free fraction and hence might be components of the apparatus of protein secretion. We have determined, by trypsin digestion and by labeling with a nonpenetrating reagent (diazoiodosulfanilic acid), the accessibility of four of these proteins on the two surfaces of the membrane, as exposed either in protoplasts or in inverted membrane vesicles. The 68-kilodalton protein is a transmembrane protein and the 45-kilodalton protein faces only the external surface, whereas the 31-kilodalton protein is inaccessible from either side. Of particular interest is the 64-kilodalton protein: it can be digested by trypsin, and can bind antibody, on the cytoplasmic surface, but only after the ribosomes have been released. This protein is thus evidently a component of the apparatus of protein secretion, closely covered by secreting ribosomes. Whether the other CM-proteins are also involved in protein secretion is uncertain.

Antigen-Antibody Complex↗
PubMed1983

Localization and quantitation of proteins characteristic of the complexed membrane of Bacillus subtilis.

We prepared antibodies to four proteins (molecular weights, 68,000, 64,000, 45,000, and 31,000) that are characteristic of the complexed (ribosome-bearing) fraction of the membrane of Bacillus subtilis and found that these proteins are immunologically distinct. Quantitation by immunoprecipitation confirmed that the ribosome-free membrane fraction contains much lower concentrations of these four proteins than the complexed-membrane fraction. The 64-kilodalton protein appeared to be attached more loosely than the other proteins, since it was more readily extracted from the membrane. In addition, this protein was also present in the cytosol in an even greater amount than in the membrane. The 68-, 64-, and 31-kilodalton proteins are present in cells in stoichiometrically equivalent amounts.

Antibodies, Bacterial↗
PubMed1983

Proteins of ribosome-bearing and free-membrane domains in Bacillus subtilis.

In lysates of Bacillus subtilis a free-membrane fraction without ribosomes can be separated from the denser membrane-ribosome complexes. As determined by one-dimensional sodium dodecyl sulfate gel electrophoresis, these two fractions differ markedly in protein composition; at least six major bands (molecular weights, 130,000, 92,000, 68,000, 64,000, 45,000, and 31,000) are essentially unique to the complexed-membrane fraction (CM proteins), and two are unique to the free-membrane fraction. After growth was slowed, the proportion of the free-membrane fraction increased, but the composition of this fraction was the same, whereas after puromycin treatment, which abruptly increased the proportion of the free-membrane fraction, this fraction contained CM proteins. Thus, it appears that the two fractions recovered from growing cells represent topographically and functionally distinct domains. In addition, the effect of growth rate suggests that formation of the complexed domain is regulated at least roughly in parallel with the formation of ribosomes. The separation of these membrane fractions should facilitate the study of protein secretion, membrane topography, and morphogenesis in bacteria.

Bacillus subtilis↗