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

Abstract

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.