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Biomedical subjects

M Vicente

Publications and source records attributed to M Vicente.

At least 73 records · Page 4Linked to original sources
PubMed1984

Co-ordination between elongation and division in Escherichia coli mediated by the wee gene product.

A procedure to construct strains of Escherichia coli containing conditional lethal mutations in two different genes was used to construct a ftsA-3(ts) wee(Am) supF(ts) strain. This strain, OV-25-7, was used to ascertain whether the wee gene product (Wee) acts at the level of regulation of cell elongation or at the co-ordination of elongation and division. The mass per unit length and the buoyant density of cells in the absence of Wee increased only if division was allowed, as in the case of strain OV-25 (wee(Am) supF(ts)), but not when it was inhibited, as in strain OV-25-7. These results suggested that in E. coli the wee gene product was acting at the level of coordination between elongation and cell division.

Cell Cycle↗
PubMed1984

The ftsA gene product participates in formation of the Escherichia coli septum structure.

The patterns of septation in filaments of Escherichia coli, formed as a consequence of the lack of an active ftsA gene product and then returned to permissive conditions, were analyzed in isogenic strains containing three different mutated alleles of ftsA. Septation was blocked for at least one doubling time at the potential septation sites that presumably contained inactive FtsA protein but not at those sites containing either the active gene product or no gene product at all. These results suggested a possible structural role for the ftsA gene product in the construction of the E. coli septum.

Alleles↗
PubMed1981

Relationship of Escherichia coli density to growth rate and cell age.

The cell densities of Escherichia coli strains B/rA, BrF, and K-12 (OV-2) were measured at several growth rates and found to be very near 1.105 g/ml in all cases. Ninety percent of the cells of any exponentially growing population banded at densities differing less than 0.75% from the mean. Synchronized populations of B/rA selected as newborn cells were found to keep their density constant for longer than one generation time. However, if selection was based on cell size, by sedimentation through a sucrose gradient, cell density was found to be almost 2% lower than that of newborn cells, but it reached normal values before the first division had taken place. These results meant that mass and volume during the lifetime of the bacterial cell followed parallel kinetics. It was unlikely that density could regulate any event of the lifetime of a cell; on the contrary, density seemed to be a physical parameter that was well controlled during the bacterial growth.

Escherichia coli↗
PubMed1980

Effect of virazole (ribavirin) on tomato spotted wilt virus in two systemic hosts, tomato and tobacco.

Virazole (1, beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide = Ribavirin), a synthetic nucleoside analogue, has been successfully used against tomato spotted wilt virus (TSWV) in tomato and tobacco plants. In tomato, the most efficient concentration to control TSWW was 500 mg/l while in tobacco, concentrations of 100 mg/l were sufficient to control systemic infection. When the plants did not show a systemic reaction virus could not be recovered from inoculated and treated tomato and tobacco plants by means of the local lesion assay. The results point out the response of a new plant virus to Virazole and indicate a possibility of controlling TSWW systemic infection.

Dose-Response Relationship, Drug↗
PubMed1980

Involvement of the ftsA gene product in late stages of the Escherichia coli cell cycle.

Strain D-3 was shown, by genetic complementation with lambda phage vectors carrying either the wild type or a temperature-sensitive allele, to contain an ftsA mutation. The presence of this mutation rendered the strain unable to divide at 42 degrees C. The action of the ftsA gene product in strain D-3 takes place at a late stage of the cycle, starting near the end of the replication cycle and extending until cell division is completed. The action of the ftsA gene product seemed to take a constant time, independent of the duration of the cell division cycle. Experiments in which all other requirements for division except a "termination protein" were completed show that cells of strain D-3 can divide under these conditions only at the permissive temperature. We conclude that a likely role for the ftsA gene product is that of a termination protein.

Bacterial Proteins↗
PubMed1980

Amber mutation affecting the length of Escherichia coli cells.

An amber mutation in a newly found gene (wee) of Escherichia coli has been isolated from strain OV-2, which harbors a temperature-sensitive suppressor. At 42 degrees C cells of the mutant, OV-25, increased in mass and deoxyribonucleic acid content and divided at normal rates, compared with the wild type under the same growth conditions. Total cell length increased under the restrictive conditions, although at a slightly lower rate. Values of mean cell length and cell volume, contrary to what would be expected from the increment in the rate of increase in particles, mass, and deoxyribonucleic acid, became at 42 degrees C smaller than those found in the wild type. A parallel increase in protein content per length and cell density and a loss of viability were found to occur after four generations at the restrictive temperature. The behavior of strain OV-25 in the absence of the wee gene product could be interpreted in terms of either a faulty regulation of the elongation processes or their abnormal coordination with the cell cycle. The genetic location of the wee gene has been found to be at 83.5 min on the E. coli genetic map.

Cell Division↗
PubMed1978

Inhibitory effect of virazole (ribavirin) on the replication of tomato white necrosis virus (VNBT).

Tomato plants (Lycopersicon esculentum Mill.) inoculated with tomato white necrosis virus (VNBT) and treated with Virazole (1-beta-D-ribofuranosyl--1, 2, 4-triazole-3-carboxamide) at a concentration of 500 mg/l developed systemic virus symptoms in only 40 per cent of the plants in which a remarkable reduction in virus concentration was also observed. From inoculated and Virazole-treated plants which had produced no symptoms, no virus could be recovered. This result suggests that Virazole may inhibit replication of VNBT in tomato.

Plant Viruses↗
PubMed1978

Cell growth and length distribution in Escherichia coli.

The length growth rate of an exponentially growing population of Escherichia coli B/r was calculated from the population length and birth length distributions. Cell elongation took place at a constant rate that doubled at a certain length. This change in rate was responsible for a sudden drop in the frequency of classes of cells longer than that length. Asymmetry in cell partition was able to generate cells both shorter and longer than the expected twofold range, but did not greatly modify the length distribution in between.

Computers↗
PubMed1976

Cell length, cell growth and cell division.

When cells of E. coli reach a certain critical length, which is constant in all growth conditions and eqqal to twice the minimum cell length, they abruptly increase their rate of elongation and divide about 20 min later. Chromosome replication terminates at about this same cell length but is not the signal for the change in rate of cell elongation.

Cell Division↗
PubMed1975

The uptake of glucose and gluconate by Pseudomonas putida.

The uptake of glucose and gluconate is under inductive control in Pseudomonas putida. Glucose, gluconate, and 2-ketogluconate were each good nutritional inducers of these transport abilities. Glucose and gluconate uptake obeyed saturation kinetics: the apparent Km for glucose was 6 mM and that for gluconate was 0.5 mM. Therefore, transport of both substrates appears to be mediated by enzyme-like carriers. Glucose and gluconate are parallel inhibitors for their uptake9 Strains selected for their inability totransport glucose were found to be deficient in gluconate uptake. The reverse was alsotrue: mutations affecting gluconate entry also blocked the uptake of glucose. These results demonstrate that a common carrier is involved in the uptake of both glucose and gluconate by P. putida cells.

Biological Transport↗
PubMed1975

The uptake of fructose by Pseudomonas putida.

Fructose transport was not apparently affected in a number of Pseudomonas putida strains with deranged activity of a common glucose-gluconate uptake system, indicating the existence of an independent fructose uptake system. Fructose uptake by glucose-gluconate uptake mutants was induced by fructose and obeyed saturation kinetics (apparent Km equal 0.3 mM). The fructose uptake system serves to transport glucose in addition to fructose. The entry of fructose into P.putida cells appears to be mediated also by the glucose-gluconate uptake system, as shown by the ability to accumulate fructose of wild type cells grown on glucose, a substrate that induces the glucose-gluconate uptake system but not the fructose uptake system. In addition, fructose was found to be an inducer of the glucose-gluconate uptake system. The physiological significance of these observations is not clear because the fructose uptake system can provide the cell with a high enough internal concentration of fructose to support maximum growth rate on this hexose, as shown by following the growth course of a glucose-gluconate uptake mutants on fructose.

Biological Transport↗