OVERLAP OF SITE OF ACTION OF X-RAY AND ULTRAVIOLET IRRADIATION IN NOCARDIA CORALLINA1

It is generally conceded that the terminal actions of X-ray and ultraviolet irradiation are mediated through different mechanisms (Hol-laender, 1954, 1955). Some differences in the cytological and genetical effects of the two ir-radiations have been found (see Swanson and Stadler, 1955, for review). However, there is accumulating evidence that there is at least an overlap between the terminal sites of action of the two radiations. Ultraviolet light has been found to have a suppressive effect on X-ray damage in yeast by Sarachek and Lucke (1953) and by Elkind and Sutton (1958, 1959), on chromosome breaks in Tradescantia pollen tubes (Swanson, 1944), and in Drosophilia sperm by Kaufmann and Hollaender (1946). This sup-pressive effect has been interpreted as indicative of site overlap by Elkind and Sutton (1959). Also, in comparisons of haploid and diploid strains of yeast, Uretz (1955) found evidence that, at least to an appreciable extent, the sensi-tive sites in the cell which are involved in both X-ray and ultraviolet irradiation are the same. The increase in X-ray sensitivity of the progeny of X-irradiated coccoids of Nocardia corallina (Clark and Webb, 1957) offers an ad-ditional approach for testing of a possible overlap of terminal sites of action of X-ray and ultra-violet irradiations. Repeated X-ray treatments of N. corallina, with several growth cycles oc-curring between treatments resulted in a sub-stantial increase in sensitivity to X rays. If ultraviolet light should cause similar results, or if populations with induced sensitivity to one ' This work was supported in part by grants from the Atomic Energy Commission under contract no. AT-(40-1)-1976, by the Facult