Species variation in transcription factor IIIA.

Species variation in transcription factor IIIA (TFIIIA) was examined by comparing the abilities of TFIIIAs isolated from different Xenopus and Rana species to 1) bind rabbit anti-Xenopus laevis TFIIIA IgG, 2) specifically interact with the Xenopus borealis somatic 5S RNA gene, and 3) promote transcription of the Xenopus borealis 5S RNA gene in vitro. In immunoblot assays, Rana catesbeiana or Rana pipiens TFIIIA did not react readily with rabbit anti-Xenopus laevis TFIIIA IgG (assayed with anti-rabbit F(ab')2 fragment conjugated with alkaline phosphatase) whereas Xenopus borealis TFIIIA exhibited similar reactivity with this IgG as Xenopus laevis TFIIIA. When compared to Xenopus TFIIIAs, Rana TFIIIAs exhibited similar interactions with the 3' portion of the intragenic control region of the Xenopus 5S RNA gene (to residue +78 on the coding strand and up to and including +74 on the non-coding strand, nucleotides protected from DNase I digestion by the N-terminal half of Xenopus TFIIIA) and incomplete interactions with the remaining 5' portion of the control region (nucleotides protected from DNase I digestion by the C-terminal half of Xenopus TFIIIA). In a Xenopus laevis unfertilized egg extract, Rana catesbeiana and Rana pipiens TFIIIAs promoted transcription of the Xenopus borealis somatic 5S RNA gene less efficiently than Xenopus laevis and Xenopus borealis TFIIIAs.