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D M PRESCOTT

Publications and source records attributed to D M PRESCOTT.

At least 19 recordsLinked to original sources
PubMed1964

THE FREQUENCY OF SISTER CHROMATID EXCHANGES FOLLOWING EXPOSURE TO VARYING DOSES OF H3-THYMIDINE OR X-RAYS.

In the Chinese hamster cell line CHEF-125, sister chromatid exchanges occurred at a rate of a little higher than one per three chromosomes for each cell cycle. The exchanges were detectable by labeling with H(3)-thymidine and autoradiographic analyses of chromosomes at the second and subsequent metaphases after labeling had occurred. To test the hypothesis that sister chromatid exchanges are caused by radiation, cells were incubated in media with different amounts of H(3)-thymidine. No statistically significant change in the exchange rate was detected over 100-fold range of variation in the amount of incorporated H(3)-thymidine (determined by grain counts of autoradiographs). We have concluded that sister chromatid exchanges are not caused by tritium radiation and therefore are spontaneous events. Cultures were also irradiated with acute doses of x-rays up to 200 r and scored for sister chromatid exchanges. Between zero and 50 r there was a statistically significant increase in the rate of exchanges. This is interpreted as evidence that x-rays can induce some exchanges, although the majority of these events are probably spontaneous.

Animals↗
PubMed1964

CELL DIVISION AND DNA SYNTHESIS IN TETRAHYMENA PYRIFORMIS DEPRIVED OF ESSENTIAL AMINO ACIDS.

The question of amino acid requirements for DNA synthesis and cell division has been studied in Tetrahymena pyriformis by depriving cells of histidine and tryptophan at defined stages in the interdivision interval. Deprivation any time before DNA synthesis does not prevent the initiation of such synthesis but completely inhibits the following division and limits the increase in DNA, as measured microspectrophotometrically, to 20 per cent. H(3)-thymidine added to the medium is not incorporated during the 20 per cent increase. Deprivation after DNA synthesis is initiated does not prevent the continuation (to completion) of DNA synthesis, and cell division ensues. H(3)-thymidine added to the medium under these conditions is incorporated into macronuclear DNA. The data indicate that some amino acid-dependent event occurs, about the time of the beginning of the DNA synthesis period, which is not essential for initiation of DNA synthesis but which is essential for the maintenance of synthesis once it has begun. These results are further discussed in terms of enzymes required to convert thymidine (and possibly the other three deoxyribonucleosides) to the immediate precursor of DNA synthesis.

Amino Acids↗