THE MATERNAL CCAAT BOX TRANSCRIPTION FACTOR WHICH CONTROLS GATA-2 EXPRESSION IS NOVEL AND DEVELOPMENTALLY-REGULATED AND CONTAINS A DOUBLE-STRANDED-RNA-BINDING SUBUNIT

The transcription factor GATA-2 is expressed at high levels in the non neural ectoderm of the Xenopus embryo at neurula stages, with lower am ounts of RNA present in the ventral mesoderm and endoderm. The promote r of the GATA-2 gene contains an inverted CCAAT box conserved among Xe nopus laevis, humans, chickens, and mice. We have shown that this sequ ence is essential for GATA-2 transcription during early development an d that the factor binding it is maternal. The DNA binding activity of this factor is detectable in nuclei and chromatin bound only when zygo tic GATA-2 transcription starts. Here we report the characterization o f this factor, which we call CBTF (CCAAT box transcription factor). CB TF activity mainly appears late in oogenesis, when it is nuclear, and the complex has multiple subunits. We have identified one subunit of t he factor as p122, a Xenopus double stranded-RNA-binding protein. The p122 protein is perinuclear during early embryonic development but mov es from the cytoplasm into the nuclei of embryonic cells at stage 9, p rior to the detection of CBTF activity in the nucleus. Thus, the accum ulation of CBTF activity in the nucleus is a multistep process, We sho w that the p122 protein is expressed mainly in the ectoderm. Expressio n of p122 mRNA is more restricted, mainly to the anterior ectoderm and mesoderm and to the neural tube. Two properties of CBTF, its dual rol e and its cytoplasm-to-nucleus translocation, are shared with other ve rtebrate maternal transcription factors and may be general properties of these proteins.