Abstract
Modification of DNA synthesis has a good reason to be expected the enhancement of radiosensitivity. Studies on the influences of aminopterin in radiosensitivity were carried out in yeast cells.
1) . Radiosensitivity of the cells depended markedly on the growing phases of the cells.
2) . Lethal effect of aminopterin treatments suggested“thmidineless death”in the experiment.
3) . Addition of TMP in the culture media following irradiation did not decrease lethality, however addition of IMP and several amino-acids together with TMP, which were considered to be inhibited by aminopterin, decreased the lethality.
4) . Some apparent discrepancies in the studies were elucidated by 2-14C-thymidine labeling experiments. In which, aminopterin treatment produced synchronization in the cell groups ; G-1 arrest in the cells harvested from log phase culture and G-2 from stationary phase culture were observed.
5) . From these experiments, some of them apparently conflicted each other, in was concluded that the cells were most radiosensitive when irradiated in late G-1 and early S. And aminopterin did not seem to enhance the radiosensitivity by 10-4mol. other than additive effect. These results suggested the utility of aminopterin combined with irradiation when adequately treated.
