RADIOACTIVE LABELING OF RNAs OF SEA URCHIN EGGS DURING OOGENESIS

¹ Division of Biology, California Institute of Technology, Pasadena, California 91109

The present experiments provide data on the results of labeling the RNA of sea urchin eggs during oogenesis, by injection of C¹⁴- and H³-uridine into the perivisceral cavity of previously spawned females. Not more than 5% of the label was found in the surrounding sea water during the first three weeks after injection. Mature eggs were obtained from animals kept for various periods of time extending to three months after injection. Optimum labeling of the RNA generally occurred at one month, at which time the eggs contained on the average some 20% of the injected label of which 95%, on the average, was in the form of macromolecules. Additional assessment, in eight of the 28 experiments of the percentage of the cold-acid-precipitable label that was in RNA gave minimum values ranging from 86 to 96%. Sucrose density-gradient centrifugation profiles of the extracted RNA showed the label to be mostly (70 to 80%) ribosomal, with about 1.5 times as much 28S as 18S RNA, and about 5 to 10% transfer RNA (45). The heterogeneously sedimenting labeled RNA, possibly messenger RNA, would amount to an upper limit of 10 to 20% of the total.