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Biomedical subjects

J Gallant

Publications and source records attributed to J Gallant.

At least 55 records · Page 3Linked to original sources
PubMed1978

A gene involved in the metabolic control of ppGpp synthesis.

A genetic locus has been identified which controls the basal synthesis of ppGpp in growing E. coli. Cells carrying a recessive allele of the relX gene have a very low concentration of ppGpp during balanced growth, and fail to accumulate ppGpp in response to carbon/energy source downshift. Moreover, the recessive relX allele renders the cells unable to grow at 42 degrees C and, when coupled with relA, makes the cells sensitive to the presence of leucine in minimal medium. RelX is cotransduced with fuc and relA and located at approximately 59.4 min on the E. coli genetic map.

Escherichia coli↗
PubMed1978

Postoperative nausea and vomiting treated with domperidone (r 33812) an open and a double-blind study.

The effect of domperidone on postoperative nausea and vomiting was evaluated in two consecutive studies. Fifty-eight patients with postoperative nausea and vomiting were included in an open pilot study and 38 other patients in a double-blind trial. In the first study 4 mg of domperidone was found to be significantly superior to 2 mg, in controlling nausea and vomiting. In the double-blind trial, vomiting recurred significantly later in domperidone than in placebo-treated patients. Side-effects were not seen nor reported in either study.

Antiemetics↗
PubMed1977

Mistranslation in E. coli.

Flagellin, the protomeric subunit of bacterial flagella, contains no cysteine. We have detected the incorporation of trace quantities of 35S-cysteine into flagellin, highly purified and then resolved by SDS polyacrylamide gel electrophoresis, to measure mistranslation in vivo. Under normal conditions, this value is about 6 X 10(-4) pmoles cysteine per pmole flagellin. This value is greatly increased during growth in low concentrations of streptomycin and neomycin, antibiotics which are known to stimulate misreading in vitro. Of the specific types of misreading which streptomycin stimulates in vitro, only misreading of the CGU and CGC arginine codons could give rise to illegitimate incorporation of cysteine. In agreement, partial arginine starvation increases the incorporation of 35S-cysteine into flagellin in a relA- mutant, with or without streptomycin, but has no such effect in its isogenic relA+ partner- Assuming from these results that 35S-cysteine incorporation into flagellin reflects misreading of CGU/C coda, we deduce a misreading probability per codon in the range of 10(-4).

Arginine↗
PubMed1977

Anomalous synthesis of ppGpp in growing cells.

In E. coli cells, accumulation of ppGpp is normally triggered by conditions that restrict the aminoacylation of tRNA or interfere with carbon/energy source metabolism; in both cases, the nucleotide's accumulation is associated with control of stable RNA synthesis and is generally believed to bring it about. We have found an anomalous situation wherein vigorously growing cells accumulate a high level of ppGpp and there is no restriction of stable RNA synthesis. This occurs when wild-type cells are shifted up from an abnormally low growth temperature to one in the optimal range (35 degrees C-40 degrees C). The effect is partly, but not entirely, dependent upon the presence of a functional relA gene product. These results appear to call into question the simpler interpretations of the role of ppGpp in the control of stable RNA synthesis.

Amino Acids↗
PubMed1977

On the translational error theory of aging.

Theoretical treatments of error feedback in translation have revealed that two different modes of behavior are possible, depending on the values of certain parameters. In mode I, the error frequency will rise steadily toward randomness, inevitably reaching whatever value is catastrophic for cell survival; the "error catastrophe" theory of aging implicitly assumes this mode of behavior. In mode II, the error frequency will converge to a stable value, which may or may not have toxic consequences. We have performed an experimental test of the behavior of the translation system in Escherichia coli cells: we altered the system's intrinsic fidelity by means of the error-promoting drug streptomycin, and monitored the kinetics of change in error frequency by means of a specific assay of one kind of mistranslation (incorporation of cysteine into flagellin). We find that the system behaves according to mode II. Moreover, E. coli cells in which the error frequency has stabilized at a value as high as 50 times greater than normal continue to proliferate, albeit abnormally slowly, and their viability is not detectably reduced. Earlier results by Gorini and his associates point in the same direction. These observations diminish the plausibility of the error catastrophe theory of aging.

Aging↗
PubMed1977

Role of the rel gene product in the control of cyclic adenosine 3',5'-monophosphate accumulation.

The presence of a relA mutant allele affects the kinetics of cyclic adenosine 3',5'-monophosphate accumulation during downshift from glucose to succinate. The nucleotide accumulates at the normal rate early in the downshift transition but continues to accumulate for a longer time in the relA mutant, leading to a two- to threefold excess by the end of the diauxic lag. Evidence is presented that this effect occurs independently of the accumulation of ppGpp.

Alleles↗
PubMed1976

A novel nucleotide implicated in the response of E. coli to energy source downshift.

When E. coli cells are subjected to energy source downshift, the accumulation of RNA (and overall cell growth) is drastically restricted within 1 to 2 min. However, the identity of the primary metabolic signal for this adjustment is a mystery. Earlier studies, and further evidence presented here, show that there is no satisfactory correlation between the sudden adjustment of RNA accumulation and the kinetics of changes in the levels of prospective signalling compounds, such as glycolytic intermediates, ppGpp, ATP, or the three adenylate nucleotides. We have discovered an unusual nucleotide, which we call the phantom spot, whose level decreases dramatically within a minute of downshift, correlating well with the adjustment of RNA accumulation. Preliminary characterization of the phantom spot indicates that it is a triphosphate derived from the guanylate pathway, and suggests that it is a form of GTP with a modification of the imidazole portion of the purine ring. We postulate that this nucleotide serves as a regulatory facsimile of ATP, linking the rate of RNA accumulation and other anabolic processes to the overall rate of phosphorylation.

Adenosine Triphosphate↗
PubMed1975

Synthesis and turnover of ribosomal ribonucleic acid in guanine-starved cells of Escherichia coli.

The relationship between the rate of RNA accumulation and the level of guanosine triphosphate was examined. Cells auxotrophic for guanine show a 6-fold drop in the intracellular level of GTP in response to the exhaustion of the exogenous guanosine supply. Contraction of the GTP pool results in a 2.5-fold reduction in the rate of RNA synthesis and the cessation of RNA accumulation. The decrease in the rate of RNA synthesis is seen to occur at the level of chain elongation. Analysis of RNA made in guanine-starved cells by competition-hybridization and sucrose gradient sedimentation suggests that the turnover of newly synthesized ribosomal RNA accounts for the observed failure of RNA to accumulate.

Escherichia coli↗
PubMed1972

A dominant constitutive phoR mutation in Escherichia coli.

A dominant constitutive mutation of the phoR locus controlling alkaline phosphatase synthesis in Escherichia coli is described. Its phenotype can be explained by the production of a poisonous subunit of the phoR gene product. The phoR gene product is inferred to consist of at least 3 or 4 subunits.

Alkaline Phosphatase↗
PubMed1971

Genetic determinant in Escherichia coli affecting thymineless death and ultraviolet sensitivity.

We have infected Escherichia coli strain B3 with F' factors carrying different lengths of the K-12 chromosome. When the F' factor carries the tsx to purE segment, the resulting hybrid merodiploid shows increased sensitivity to thymineless death, although leaky deoxyribonucleic acid synthesis is unaffected, as well as increased sensitivity to ultraviolet irradiation. The dominant or partially dominant character of the effect indicates that it is not a product of allelic differences between E. coli K and B at either ras or lon.

Adenine↗