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B D Davis

Publications and source records attributed to B D Davis.

At least 109 records · Page 6Linked to original sources
PubMed1974

Activity of colicin E3-treated ribosomes in initiation and in chain elongation.

Colicin E3 (called E3 here) is shown to act on polysomal ribosomes as well as on free ribosomes. This treatment severely inhibits subsequent chain elongation, both on preformed polysomes completing their nascent chains and on ribosomes translating poly(U). Elevated Mg(++) concentration relieves this inhibition. However, elevated Mg(++) concentration does not relieve the inhibition of ribosomes initiating on natural messenger; hence damage by E3 appears to have an additional, specific effect on some stage in initiation. The effect of damage by E3 resembles that of streptomycin in several respects. This similarity suggests that the two agents may act on closely related sites on the ribosome.

Bacterial Proteins↗
PubMed1974

Selective inhibition of initiating ribosomes by spectinomycin.

Spectinomycin at low concentrations inhibits initiating ribosomes but not ribosomes already engaged in chain elongation. The initiating ribosomes are blocked in some step after formation of the initiation complex, probably the first translocation. Cells inhibited by spectinomycin accumulate polysomes, and these have proved to be unstable polyinitiation complexes: they can be pulse-labeled with methionine but not with valine, and they disappear after addition of rifampicin. Hence, the blocked ribosomes evidently are released and then reinitiate. In heterozygotes this cyclic reinitiation by the sensitive ribosomes, each blocking an initiation site for an average of 10-15 min, can explain (just as with streptomycin) the dominance of sensitivity over resistance.

Bacterial Proteins↗
PubMed1973

Partial inhibition of polysomal ribosomes of Escherichia coli by streptomycin.

With purified initiation-free polysomes of E. coli, whether endogenous or formed in vitro on phage R17 RNA, streptomycin causes partial inhibition of chain elongation. The degree of inhibition is constant over a broad range of streptomycin concentration and decreases markedly with increasing Mg(++) concentration. Hence, streptomycin evidently complexes readily with polysomal ribosomes, causing a partial block in chain elongation. Streptomycin has already been shown to cause a complete block of chain elongation by free ribosomes forming initiation complexes in its presence. The production of a different effect on polysomal ribosomes explains how streptomycin can exert two mutually exclusive effects in cells: phenotypic suppression at low concentrations and irreversible inhibition of protein synthesis at higher concentrations. It also becomes possible to understand why killing by streptomycin is antagonized by agents (such as chloramphenicol) that cause a stable blockade of the ribosomes in polysomes.

Carbon Isotopes↗
PubMed1972

A ribosome dissociation factor from rabbit reticulocytes (fluoride-E. coli ribosomes-initiation factors).

A ribosome dissociation factor has been detected in an extract of ribosomal particles from rabbit reticulocytes. This factor dissociates free ribosomes from reticulocytes and also from Escherichia coli; it does not dissociate ribosomes complexed with peptidyl-tRNA and mRNA. The reaction appears to be stoichiometric rather than catalytic; it reaches completion in one minute at 37 degrees C, but is very slow at 0 degrees C, and it is antagonized and reversed by Mg(++). Reticulocyte dissociation factor thus closely resembles that from E. coli. However, the activity has been found primarily associated with the native large subunits rather than the small subunits in lysates.

Animals↗
PubMed1972

Bactericidal action of streptomycin and comparison with spectinomycin in heterozygotes of Escherichia coli.

Str(s)/str(r) heterozygotes of Escherichia coli K-12 are shown to be sensitive to the lethal as well as the inhibitory action of streptomycin. The rate of killing was lower in heterozygotes than in sensitive homozygotes, and among heterozygotes it was lower in those with a higher proportion of resistant ribosomes. These strains also differed, in a parallel manner, in the kinetics of inhibition of growth and protein synthesis by streptomycin. Similar results were obtained with spectinomycin and corresponding merodiploid strains. Since spectinomycin is purely bacteriostatic and stabilizes polysomes, it must block resistant ribosomes behind inhibited sensitive ribosomes; hence, these results are consistent with an initial similar polysomal blockade by streptomycin. However, since streptomycin causes gradual polysome breakdown, its dominant lethal action must involve some mechanism other than a permanent polysomal blockade.

Antibiotics, Antineoplastic↗
PubMed1971

Rapid exchange of subunits between free ribosomes in extracts of Escherichia coli.

The runoff of a mixture of "heavy" and "light" polysomes has been reported to yield hybrid ribosomes, of intermediate density. However, we found that the dissociation of free heavy ribosomes as they advance in a sucrose gradient causes a serious artefact in the demonstration of hybrid ribosomes. This artefact is eliminated by fixation with glutaraldehyde before sedimentation. Formation of hybrid ribosomes can then be demonstrated, but it is equally complete whether the heavy and light preparations are mixed before or after runoff. Hence, free ribosomes exchange subunits rapidly in extracts. The previously reported exchange thus does not provide evidence for formation of free subunits during runoff.

Aldehydes↗
PubMed1971

Growth rate of Escherichia coli at elevated temperatures: limitation by methionine.

When Escherichia coli growing in minimal medium is shifted from 37 C to any temperature in the range 40 to 45 C, the growth rate immediately assumes a new, lower value, characteristic of that temperature. The decrease is shown to be due, in several strains, to decreased activity of the first enzyme of the methionine pathway, homoserine trans-succinylase, which thus appears to be more heat-sensitive than any other essential enzyme in the cell. This sensitivity does not involve progressive denaturation of the enzyme; rather, the response to a shift of temperature, in either direction, is immediate and reversible.

Acyltransferases↗