PubMed Health⌕ Search

Biomedical subjects

E C POLLARD

Publications and source records attributed to E C POLLARD.

15 recordsLinked to original sources
PubMed1965

IONIZING RADIATION: EFFECT OF IRRADIATED MEDIUM ON SYNTHETIC PROCESSES.

The incorporation of uracil-C(14) into macromolecules in Escherichia coli cells is decreased by doses of ionizing radiation when the cells are in very dilute suspension. The decrease results from an action of irradiated medium on the cells, and a similar reaction is observed during the incorporation of thymine (indication of DNA synthesis) and of proline and valine (indicative of protein synthesis). Irradiated medium reduces the formation of beta-galactosidase but does not cause the degradation of DNA.

Carbon Isotopes↗
PubMed1964

IONIZING RADIATION: EFFECT ON GENETIC TRANSCRIPTION.

Cells of Escherichia coli grown on maltose can be induced by the addition of thiomethyl galactoside to produce beta-galactosidase. If cells are irradiated shortly after induction, the transcription of the DNA ceases, and the enzyme produced by the messenger RNA is observed to reach a maximum. From these data the calculated half-life of unstable messenger RNA is given over a temperature range from 8.1 minutes at 10 degrees C to 0.7 minute at 45 degrees C. The kinetics of cessation of transcription give information on both meassenger RNA decay and rate of transcription. Arrhenius graphs for both these rates are given, and the activation energies mtieasured are 11,000 calories per mole for decay and 22,000 calories per mole for transcription. This relation to temperature is characteristic of enzymatic behavior.

DNA↗
PubMed1964

RADIATION ACTION ON DNA IN BACTERIA: EFFECT OF OXYGEN.

In Escherichia coli cells ionizing radiation produces a degradation of DNA to approximately 50 percent of the total amount originally insoluble in trichloroacetic acid. There is also a reduction of synthesis. Oxygen inhibits the degradation process by a dose reduction factor of 4 and the synthesis process by a factor of approximately 1.5. Thus, at relatively low doses, radiation action on bacteria is very probably mediated through the DNA.

Carbon Isotopes↗
PubMed1961

Radiation inhibition of amino acid uptake by Escherichia coli.

The inhibition of macromolecular synthesis in Escherichia coli by ionizing radiation has been investigated. The survival of the ability to incorporate arginine, leucine, isoleucine, histidine, uracil, and glucose after various doses of gamma radiation, deuteron and alpha particle bombardment has been measured. All amino acids are incorporated by processes which show the same radiation sensitivity. The sensitivity of uracil corresponds to a volume which is roughly spherical, of radius about 160A, whereas the amino acids possess sensitive regions which are long and thin in character. The uptake of glucose is concerned with a smaller, roughly spherical unit. The possible identification of the radiation-sensitive targets with cellular constituents is discussed. The long thin character observed for amino acids suggests that the sensitive region affected by radiation is an unfolded form of a ribosome, or alternatively a long nucleic acid molecule. For uracil the sensitive region fits with a 70S ribosome, while for glucose a smaller particle would fit the data.

Amino Acids↗
PubMed1959

Correlation of physical and biological properties of mouse mammary tumor agent.

Biophysical procedures have been used to determine the size and structure of the biologically active agent responsible for the transmission, through milk, of mouse mammary adenocarcinoma. Filtration of milk from RIII high-breast-cancer mice through gradocol membranes with decreasing pore sizes indicated that a minimum of activity passed through intermediate pore sizes (100 to 160 mmicro). Filtrates through smaller pores were significantly active. Milk treated with small doses of deuteron irradiation produced more tumors than the control, unirradiated milk; larger doses indicated a particle size much less than 100 mmicro. Free diffusion experiments indicated that the activity was associated with particles of two different sizes. Altogether the data denoted the presence of a large agent about 100 mmicro in diameter and a small agent 20 to 30 mmicro in diameter or possibly smaller. Furthermore, the presence in the milk of an inhibitor 40 to 60 mmicro is indicated by the results of all three approaches. The complex nature of the milk agent disclosed by the physical measurements agrees with the picture of one of the structures revealed by electron microscopy as well as with seemingly conflicting measurements reported in the literature. The large agent defined by these indirect methods corresponds to the whole particle seen in the electron microscope and the small agent corresponds to its internal core or nucleoid. It is suggested that the nucleoid is essentially a nucleic acid which may, in the absence of the "inhibitor," retain its activity after being stripped of its outer membrane or sac.

Animals↗
PubMed1959

Production of the milk agent in cultures of mouse mammary carcinoma.

Thin sections of tissue cultures grown from tumors of the RIII high-breast-cancer strain mice were studied in the electron microscope. These tissues contain an abundance of particles whose morphology is consistent with biophysical measurement of the milk agent. These particles, found only extracellularly in our cultures, are formed at the cell membrane. The process of formation, as reconstructed from sections, appears to include a thickening and protrusion of the cell membrane which then evolves gradually into a dense sphere and separates from the cell in much the same manner as does influenza virus. The contents of the newly formed body are later rearranged to form a nucleoid within a membranous sac.

Animals↗