EFFECTS OF DISINTEGRATIONS OF PHOSPHORUS-32 INCORPORATED IN THE YEAST SACCHAROMYCES CEREVISIAE. I. INDUCTION OF A MUTATION TOWARD RESISTANCE TO THE LETHAL EFFECT OF X RAYS (in French)
The effects of P/sup 32/, added as H/sub 3/PO/sub 4/ to the culture medium, and of x rays, applied at rates of 15 to 80 kr/min, were tested on haploid and diploid strains of the yeast. The survival curve of haploid yeast cells to P/sup 32/ decay was exponential. No tailing off of the dose-response curve was seen, contrary to what occurs with x rays. The P/sup 32/ lethal effect was not modified by starvation, which decreases the RNA content of the cells. The site sensitive to P/sup 32/ disintegrations may therefore be DNA. During the decay, the yeast population becomes more and more resistant to the lethal effect of x rays. It was shown that this is not the consequence of a selective process, but the induction of radioresistance in previously sensitive cells. Clones derived from the survivors of P/sup 32/ decay were stable as regards their resistance to x rays. After a decay which leaves approximates 1 out of 100 living cells, nearly all survivors yield resistant type clones. The survival curves to x rays of most of the resistant mutants are sigmoidal, with a final slope smaller by a factor of 2 to 3 than that of the sensitive strain. With alpha rays the difference in the slope is the same as with x rays, but the curves are exponential. This resistance is not affected by growing the cells in complete or in minimal mineral medium prior to irradiation. The induced resistance to x rays appears with the same efficiency whether the P/sup 32/ decay occurs before or after irradiation of the cells. This rules out the possibility that the structure involved affects some process contemporary with the primary effect of x rays. The resistant character applies to both x and alpha rays but not UV or P/sup 32/ decay. In addition, no additional increase in radioresistance is obtained by labeling a resistant strain with P/sup 32/. A radiosensitizing oxygen effect of the same magnitude was observed for both sensitive and resistant cells. The increase in radioresistance relates only the lethal action. No effect was observed on induction of mutation to prototrophy for three auxotrophic characters (His/sup -/, Try/sup -/, Ad/sup -/). The resistant mutants were haploid, according to their normal DNA content and to genetic analysis involving segregation of suitable markers. Radiosensitivity (S/ sup +/) was dominant over radioresistance (S/sup -/) for diploid cells (S/sup -/S/ sup +/) resulting from a cross. These diploids were less resistant than the resistant haploid parent but more resistant than the haploid wild type. Their survival curve was identical to that of the diploid wild type. By the random sporulation technique of a S/sup -/S/sup +/ strain, it was shown that the resistant character segregates from the sensitive one with a ratio of l: 1. It was not linked to any of the three metabolic markers used in this study. The efficiency of P/sup 32/ decay in inducing resistance to x rays corresponds to a target whose max size (assuming that it is DNA) is about 1/20 of the whole genome. It is suggested that the S/sup +/ character is linked to a selfreproducing phosphorus-containing structure whose location and function in the cell are unknown. (BBB)
- Research Organization:
- Institut Pasteur, Paris
- NSA Number:
- NSA-17-037072
- OSTI ID:
- 4647686
- Journal Information:
- Ann. Inst. Pasteur, Vol. Vol: 103; Other Information: Orig. Receipt Date: 31-DEC-63
- Country of Publication:
- Country unknown/Code not available
- Language:
- French
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