Xenopus transcription factor IIIA (XTFIIIA): after a decade of research.

Xenopus transcription factor IIIA (XTFIIIA) is the first eukaryotic transcription factor purified to homogeneity and is specifically required for the 5S RNA gene transcription. It contains two structural domains and nine zinc finger motifs through which it recognizes the promoter region of the 5S RNA gene. It also binds to 5S RNA and serves to store 5S RNA in the form of 7S ribonucleoprotein particles in oocytes. Additionally, it forms a metastable complex with 5S DNA and promotes the formation of stable and competent transcription complexes. Its expression is developmentally controlled at the level of transcription and translation. Moreover, it participates in the assembly of active chromatin templates and at least, in part, is responsible for the developmental regulation of two kinds of 5S RNA genes in Xenopus.