The role of DNA-mediated transfer of TFIIIA in the concerted gyration and differential activation of the Xenopus 5S RNA genes.

The transcription factor of the 5S RNA gene, TFIIIA, induces gyration of oocyte- and somatic-type 5S DNA plasmids in Xenopus oocyte extracts, but oocyte 5S gyration requires a 5-fold higher TFIIIA concentration than somatic 5S gyration. Concomitant with the differential gyration at intermediate TFIIIA concentrations, the oocyte genes are repressed and the somatic genes become activated, a situation that mimics the one seen in Xenopus somatic cells. Data obtained with plasmids immobilized in agarose indicate that TFIIIA finds its site via a DNA-mediated transfer mechanism, and that all-or-none gyration is a consequence of TFIIIA transfer between 5S DNA sites. Based on these results, we present a model that explains the differential all-or-none activation of the 5S RNA genes.