Bioassay for components regulating eukaryotic gene expression: A chromosomal factor involved in the generation of histone mRNA 3' termini

We have adapted the oocyte injection procedure for the detection of regulatory components involved in the transcription of a eukaryotic mRNA gene. Injection of the histone gene repeat h22 DNA of Psammechinus miliaris into the Xenopus oocyte nucleus results in correct initiation of the histone mRNAs, but readthrough by RNA polymerase occurs at the 3' end of the H3 histone gene. Coinjection into the oocyte of a chromosomal salt wash fraction derived from sea urchin embryos results in the generation of authentic 3' termini of the histone H3 mRNA. We have partially purified the protein component by column chromatography and density gradient centrifugation. The regulatory factor binds to heparin columns and, hence, has the properties anticipated of an RNA- or DNA-binding protein. The sedimentation coefficient of the active component was determined to be about 12 S, suggesting a molecular weight of 200,000-250,000.