TRANSCRIPTION FACTOR-IIIA (TFIIIA) - AN UPDATE

Xenopus transcription factor, termed TFIIIA, is the first eukaryotic t ranscription factor purified to homogeneity and one of the most extens ively characterized polymerase Ill gene factors at the levels both of the protein and its gene. It is an abundant protein in oocytes and is specifically required for the 5S RNA gene transcription. It promotes t he formation of a stable transcription complex by first binding to the internal control region of the 5S RNA gene through its zinc finger mo tifs. It contains two structural domains and associates with 5S RNA to form 7S ribonucleoprotein particles in oocytes. Its expression is dev elopmentally controlled at the level of transcription and translation. It participates in the assembly of active chromatin templates and, at least in part, is responsible for the differential expression of two kinds of 5S RNA genes in Xenopus.