ISOLATION FROM XENOPUS-LAEVIS EMBRYONIC-CELLS OF A FACTOR WHICH STIMULATES RIBOSOMAL-RNA SYNTHESIS BY ISOLATED-NUCLEI

When oocyte extracts are fractionated by G-100 Sephadex and then DEAE-cellulose chromatography they yield four activities which stimulate RNA synthesis in isolated Xenopus nuclei. Three affect all polymerase activities, producing stimulations of five- to eight-fold. The fourth specifically stimulates rRNA synthesis by over 20-fold. The amount of rRNA made is so large that the rate of initiation must be increased. The rRNA-specific factor and one of the nonspecific factors are greatly reduced in extracts of eggs. They return to normal levels at the late blastula stage of development, and remain abundant through later stages. These changes may be related to the greatly reduced transcriptional activity seen in eggs and preblastula embryos, and the activation of RNA synthesis at the blastula stage of development. © 1979.