Differential 5S RNA gene expression in vitro.

In extracts derived from activated eggs of Xenopus, oocyte 5S RNA gene transcription complexes are destabilized under conditions where somatic 5S RNA gene transcription complexes are stable. Trans-acting factors in destabilized complexes are in equilibrium with free factors in the extract, and thus transcription becomes dependent upon the concentration of the limiting factor in the extract. By reducing TFIIIA, a limiting factor in the egg extract, a cloned somatic 5S RNA gene is transcribed as much as 400-fold more efficiently than a cloned oocyte 5S RNA gene.