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It is now established that X-radiation affects the cells by inhibiting colony formation1 and by de­ creasing the nucleic acid synthesis 2 etc. Limited obser­ vations, however, have been made on the effect of X-radiation on the cytoplasmic component ‘ribosomes’ which are a combination of nucleic acid and protein and are also the site of protein synthesis of the cell 3. The effects of X-radiation on ribosomes of E. coli4> 5 showed disruption of some components with high dose. This communication reports the results of in vivo Xirradiation on the ribosomes of yeast cells by comparing the ultracentrifugal distribution of various cytoplasmic components which are S-RNA, S-protein and ribosomes. A selected strain of Saccaromyces cerevisiae was maintained in slants containing one percent peptone, four percent maltose in distilled water at about pH 5 and 2.3 percent agar. Before an experiment, the cells were taken from three fresh slants and inoculated into 600 ml liquid media (1% peptone, 4% maltose, pH 5) and cultured anaerobically at 30 °C. After 5 hrs of growth, log-phase cells were separated from the me­ dium by centrifugation, washed twice with sterile physiological saline and collected with 1 0 ml saline. This cell suspension was divided into two 5 ml parts. One part was kept in ice as control. The other part was irradiated to the desired dose in the cold with a con­ tinuously operated X-ray machine running at 80 kV. The dose rate at the point of irradiation, measured with a Victoreen r-meter, was 5 x 103 Rad/min. Three sets of experiments were done. In all cases about 2 x 108 log-phase cells contained in 5 cc. normal saline were irradiated in the cold. The irradiation and subsequent treatment of the cells were according to the details given in columns 2 and 3 of the following table. The cytoplasmic extract was made after the treatment mentioned in the last column. After scheduled treatment, the crude extract was prepared from the cells according to the method of C h ao 6. The cells were collected from the medium by centrifugation and washed with the buffer. They were collected with a few ml of buffer 0.002 m KH2P04 — K2HP04 (1:4) + 0,001 m MgS04 in such a way that the number of cells present per ml of buffer remained the same in the control and in the irradiated experi­ ments to ensure comparable concentration of the ex-

Notizen: Effect of X-radiation on the Ribosomes of Yeast Cells