Xenopus 5S gene transcription factor, TFIIIA: characterization of a cDNA clone and measurement of RNA levels throughout development.

Initiation of 5S RNA gene transcription in Xenopus oocytes requires a 38,500 dalton polypeptide, TFIIIA. The levels of both 5S RNA and TFIIIA are regulated throughout oogenesis and embryonic development. To delineate the mechanisms by which the corresponding genes are regulated, as well as to determine the primary structure of TFIIIA, we have isolated a cDNA clone that encodes TFIIIA. Using the cDNA clone, we have determined that there is (are) one or a small number of TFIIIA gene(s) per Xenopus haploid genome, and we have estimated the size and levels of TFIIIA RNA throughout Xenopus development. We report sequence homologies between TFIIIA cDNA and regulatory regions of the Xenopus tmet and 5S RNA genes. Implications of these data for developmental regulation of the TFIIIA and 5S RNA genes are discussed.