INHIBITOR OF RIBOSOMAL RNA SYNTHESIS IN XENOPUS LAEVIS EMBRYOS .I. CHANGES IN ACTIVITY OF INHIBITOR DURING DEVELOPMENT AND ITS DISTRIBUTION IN EARLY GASTRULAE

Inhibitor preparations from Xenopus laevis embryos of different developmenlal stages and from different regions of early gastrulae were assayed on the activity to inhibit ribosomal RNA synthesis in isolated cells of tail bud embryos. The activity decreased in the following order: mid-blastulae (stage 8), early gastrulae (stage 10) and mid-gaslrulae (stage 12), and vegetal, ventral and dorsal regions. Rates of ribosomal RNA synthesis were also measured and found to increase in the exactly reverse order. These findings may be interpreted as indicating that the inhibitor is, as has been suggested, involved in the regulation of ribosomal RNA synthesis during the development. © 1968.