Inhibitor of ribosomal RNA synthesis in Xenopus laevis embryos : V. Inability of inhibitor to repress 5S RNA synthesis

Abstract

A specific inhibitor of ribosomal RNA (rRNA) synthesis was partially purified from an acid-soluble fraction of Xenopus laevis blastulae. Effects of this inhibitor on 5S rRNA synthesis of isolated neurula cells of the same species were investigated. The results show that the synthesis of both 5S rRNA and 4S RNA proceeds normally when both 18 and 28S rRNA are almost completely inhibited. Failure of the inhibitor to suppress 5S rRNA synthesis suggests that it plays an important role in the regulation of 18 and 28S rRNA synthesis during development and that the synthesis of 5S rRNA is not coordinated to that of 18 and 28S rRNA.