Association of a 5S gene transcription factor with 5S RNA and altered levels of the factor during cell differentiation.

We have previously purified from Xenopus ovaries a protein factor (TF IIIA) which is necessary for the accurate in vitro transcription of 5S RNA genes. We now report that this factor (a 5S gene transcription effector) is identical by immunological, chemical and functional criteria to the protein associated with 5S RNA (the gene product) as a 7S ribonucleoprotein (RNP) complex in immature oocytes. After oocyte maturation, TF IIIA is no longer detectable functionally or immunologically in unfertilized eggs, which do not synthesize 5S RNA in vitro. Moreover, we cannot detect TF IIIA immunologically in extracts fron Xenopus somatic cells which, nevertheless, efficiently transcribe 5S genes.