The Loci of Action of Ultra-Violet and X-Radiation, and of Photorecovery, in the Egg and Sperm of the Sea Urchin

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Abstract
Whole eggs of Arbacia punctulata were exposed to u.-v. radiation either before or after fertilization with normal sperm. Eggs were also separated by centrifugation into nucleate and enucleate halves, and each part was exposed before or after fertilization. In other cases, sperm were exposed before being used to fertilize the eggs or their halves. Results of several expts. showed that a delay in cleavage occurred in all cases except when the enucleate half of the egg was exposed to u.-v. radiation before fertilization with normal sperm, thus indicating that the locus of action of the radiation was associated with the nucleus. Similar expts. showed that the return toward the normal cleavage rate was increased by illumination with visible radiation and that the egg cytoplasm was essential for the photorecovery process. In expts. with X-rays the delay in cleavage was associated with the nucleus but visible radiation did not accelerate recovery. Photorecovery after u.-v. radiation is compared to photoreactivation in fungi and bacteria, especially with reference to bacteriophage and Escherichia coli. It is believed that the nucleoprotein in the nucleus is the absorber of u.-v. radiation in the primary photochemical act leading to cleavage delay.