d Gnioersity, Califomin SIX FIGURES
Studies on photoreactivation, tlie reversal of injurious effects of ultraviolet radiation by illumination with visible light (Keliier, '49a), have been concerned mainly with viability and niutations (Kelner, '49a, b ; Dulbecco, '49 ; Kovick and Szilard, '49) but some studies on the retardation of division have appeared (Blum, '49 ; Marshak, '49). The mechanism of photorcactiviation is still obscure. Studies on other processes in the cell might be expected to add data which ~o u l d be useful in elucidating the mechanism of action of the light. No studies on photoreactivation in particular enzymatic systems in the cell have yet appeared. Preliniinar$ studies shoswcl that the formatioii of galactozymasc, an adaptive enzyme in yeast, mas readily inhibited by ultraviolet radiation. Studies of this adaptation process therefore offered an opportunity for testing diether cells so inhibited could be photoreactivatccl. The experiments reported belo~v show that yliotoreactivation is possible and the implicatioiix of the experiments are discussed.
MATERIALS AXD 3lRTHODS
SaccFmromyces cereviseae of a strain obtained from the University of Toronto was grovn on 1% peast extract. 2% glucose and 27. agar in an incubator at about 30ยฐC. and thc cultures werp used after 24 hours incubation. The yeast qromtli was washed from the plate with distilled water and Supiprted in part by grants from the Bockefcllrr Foandntion.
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' The maintenance of gnlaetozgrnase in yeast after irradiation was riot studied.
Howexer it is likely that it would not be replaced and that the irradiatcd sampIes of yeast mould show a lesser capacity t o utilize galactose, similar to the decline seen in the use of glucose by yeast after irradiation (Giese and Swanson, '47).