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Biomedical subjects

A B Pardee

Publications and source records attributed to A B Pardee.

At least 253 records · Page 14Linked to original sources
PubMed1970

Animal cells: noncorrelation of length of G1 phase with size after mitosis.

The interval between mitosis and initiation of DNA synthesis (G(1)) varied over a fourfold range for Chinese hamster ovary cells, an established line. This was not because of size differences. Synchlronous cells of different sizes began DNA synthesis at similar times after mitosis. A novel technique of centrifugation for separating cells according to size is described.

Animals↗
PubMed1970

Requirement of polyamines for bacterial division.

Synchronous cell division in an arginine auxotroph and a histidine auxotroph of Escherichia coli was obtained after starving for the required amino acid for 1 hr. However, cell division was not synchronized after starvation for 1 hr in another arginine auxotroph. This difference is proposed to depend on differences in the concentrations of polyamines in the cells. During amino acid starvation the ratio of putrescine concentration to spermidine concentration decreased in all strains, but it recovered afterward more rapidly in the third strain than in the other two. The cells divided when the ratio returned to normal in the Arg(-) mutants. Added putrescine permitted some of the cells of the first two mutants to divide sooner after amino acid starvation and thus eliminated synchrony. Spermidine added alone had no effect, but, when it was added together with putrescine, it restored synchronous division. Synchrony was established in the third mutant by adding spermidine after arginine starvation. Thus, both the variations in polyamine content and the effects of added polyamines suggest that the polyamines are essential in permitting cell division. We suggest that the molar ratio of putrescine to spermidine can be a critical factor for cell division. This effect of polyamines seems to be specific for cell division. Amino acid starvation does not induce delays in subsequent mass increase or deoxyribonucleic acid synthesis. Possible mechanisms of polyamine action are discussed.

Amines↗
PubMed1970

Accumulation of a protein required for division during the cell cycle of Escherichia coli.

A heat-labile protein required for division accumulates during the duplication cycle of Escherichia coli. Its formation appears to commence shortly after the cell divides, and it reaches a maximal amount shortly before the next division. A plausible mechanism for timing cell division depends on building up the critical amount of this protein. Completion of deoxyribonucleic acid (DNA) replication is also necessary for division to occur, but it does not uniquely initiate division. The evidence for these conclusions comes from heat-shock experiments; heating to 45 C for 15 min delays division increasingly with the age of a cell. A heat shock given near the end of a cycle delays division for about 30 min, whereas at the beginning of the cycle it hardly affects division. The net result is synchronization of cell division. The effect of heat is increased in bacteria which have incorporated p-fluoro-phenylalanine into their proteins. When the incorporation is early and the heat shock is late in the cycle, division is delayed by about 30 min, indicating that the division protein is synthesized early even though its sensitivity is not observed until later. At any time in the cell cycle, heat shock simply delays total protein and DNA synthesis ((3)H-thymidine uptake) for approximately 14 min. DNA replication and cell division are thus discoordinated, since DNA replication is not synchronized by the treatment.

Bacterial Proteins↗
PubMed1969

Transport changes rapidly initiated by serum addition to "contact inhibited" 3T3 cells.

Two- to fourfold increases in uridine and phosphate uptake were brought about within 10 to 15 minutes after adding fresh serum to confluent 3T3 cells. The stimulation of transport was specific, since no serum effect was observed for 3-O-methyl-D-glucose or amino acids. The early increase in RNA labeling, previously identified by (14)C-uridine incorporation, could be accounted for by this transport effect. Increased labeling with (32)P-phosphate of at least five phospholipids occurred soon after adding serum. This increase, however, could not be accounted for by increased transport. Both of these results suggest that specific early membrane changes are involved in "contact inhibition."The following results are consistent with this suggestion. Uptake of uridine and phosphate by nonconfluent 3T3 cells was higher than by confluent cells and was only slightly increased by fresh serum. In contrast, uptake of these substrates by Polyoma virus-transformed 3T3 cells, which are not subject to "contact inhibition," was not significantly decreased after the cells became confluent, and serum addition had no effect on transport by either nonconfluent or confluent Polyoma virus-transformed 3T3 cells. Fractionation of serum on Sephadex G-200 demonstrated that the factor which stimulated phosphate transport was different from the previously identified factor which stimulates DNA synthesis by confluent 3T3 cells.

Animals↗
PubMed1968

Evidence for a relationship between deoxyribonucleic acid metabolism and septum formation in Escherichia coli.

Septum formation is a key step in bacterial division, but the mechanism which controls periodic septum formation is unknown. In an attempt to understand this mechanism, lon(-) mutants, in which septum formation is blocked by very doses of ultraviolet light (UV), were investigated. UV must act on some part of the apparatus of cytokinesis; thus, identification of the UV target would identify part of this apparatus. As likely possibilities, UV might damage the septum-forming site or it might damage deoxyribonucleic acid (DNA), since DNA replication is normally coordinated with septum formation. To distinguish between these possibilities, DNA was specifically sensitized by incorporating bromodeoxyuridine into lon(-) bacteria. These bacteria were strongly sensitized to longer wavelength UV (2,900 to 3,100 A) so that they failed to form septa, grew into filaments which lysed, and did not form colonies. Various control experiments supported the conclusion that UV inhibits septum formation as a result of alterations in DNA metabolism. A relationship thus exists between DNA metabolism and septum formation.

Bromodeoxyuridine↗
PubMed1968

Location of sulfate-binding protein in Salmonella typhimurium.

A method is described for location of proteins in bacteria. It depends upon two techniques. One technique is the inactivation of the protein by a reagent which is incapable of penetrating the bacterial membrane (permeability barrier). Proteins inside this membrane cannot be inactivated unless the cells are disrupted; proteins on or outside the membrane can be inactivated. The second technique depends upon inactivation of the protein by specific antibody. Antibody should not penetrate the external bacterial wall, and therefore should only inactivate proteins that are on the wall surface. Thus, proteins can be localized inside the membrane, in the wall-membrane area, or outside the wall. One reagent developed for use with the first technique is diazo-7-amino-1,3-naphthalene-disulfonate. It inactivated beta-galactoside transport, but not beta-galactosidase of intact Escherichia coli. Similarly, it inactivated sulfate binding and transport but not uridine phosphorylase activity of Salmonella typhimurium. This indicates that the sulfate-binding protein is on or outside the cell membrane, and that uridine phosphorylase is inside the cell. The organic mercurial compounds used also showed that the sensitive parts of the sulfate and alpha-methylglucoside transport systems are less reactive than the sensitive part of the beta-galactoside system. Antibody to the sulfate-binding protein inactivated the purified protein but did not inactivate this protein when intact bacteria were employed. Thus, it appears that the sulfate-binding protein does not protrude outside the cell wall. The conclusion that the binding protein is located in the wall-membrane region is supported by its release upon spheroplast formation or osmotic shock, and also by its ability to combine with sulfate in bacteria which cannot transport sulfate into the cell.

Azo Compounds↗
PubMed1967

Conditional mutations involving septum formation in Escherichia coli.

The lon(-) mutation is responsible for a defect in cell division of Escherichia coli lightly irradiated with ultraviolet light (UV). These lon(-) mutants can be isolated readily by a procedure described here. Physiological studies were performed with the objective of determining the role of the lon gene. Unirradiated lon(-) mutants grow normally, except that a correlation of this mutation with capsule formation has been noted previously. These two properties can be separated, however. After irradiation, lon(-) grows as long filaments because septum formation is prevented. The filaments eventually lyse. Mass increase and deoxyribonucleic acid and enzyme synthesis appear to proceed normally. Thus, the lesion produced by UV appears to be highly specific. In bacteria that carry both genes (merozygotes), lon(+) is dominant to lon(-). Septum formation is restored to irradiated lon(-) bacteria by introduction of lon(+) by conjugation. Also, normal growth can be restored by nutritional variations. It is concluded that lon(+) is able to nullify the effects of the UV lesion under conditions where lon(-) cannot. Possibly, capsule precursors that can accumulate in the latter are responsible for the difference because they interfere with repair of the UV lesion.

Bacteriolysis↗
PubMed1967

Ultraviolet-sensitive targets in the enzyme-synthesizing apparatus of Escherichia coli.

Inhibition by ultraviolet light of beta-galactosidase and alkaline phosphatase synthesis was investigated in both ultraviolet (UV)-sensitive and UV-resistant (wild-type) Escherichia coli, with the objective of determining the sensitivity of various targets. Kinetics of enzyme formation by unmated bacteria and in mating systems, in which the donor provided the specific genetic material and the recipient the cytoplasm, permit the following conclusions regarding the sensitivity of various targets. Catabolite repression resulting from UV damage causes most of the inhibition of beta-galactosidase formation. When it is largely eliminated by a step-down in nutrition, the principal target in UV-sensitive bacteria appears to be the structural gene (lacZ(+)), but damage to the cytoplasm is also important. Transitory inhibition by inactivation of messenger ribonucleic acid is also observed. In wild-type bacteria, repair reduces the importance of lesions in deoxyribonucleic acid sufficiently that cytoplasmic damage appears to be at least as important. Repair occurs within 10 min, as shown by recovery of enzyme-synthesizing ability. Caffeine and proflavine prevent recovery. Newly mated bacteria respond to irradiation very differently than do unmated bacteria. The beta-galactosidase or alkaline phosphatase structural gene (lacZ(+) or phoP(+)) is much more inhibited after it is transferred than it is in unmated bacteria. This sensitivity seems to depend on a sensitive state of the injected material, rather than on a different physiological condition of the entire zygote. Irradiation of recipient uvr(+) bacteria much more strongly inhibited expression of injected genes than if the F(-) was uvr(s). Studies on mating systems are not very useful for learning about the function of unmated bacteria.

Acridines↗