CLONING AND CHARACTERIZATION OF A NUCLEAR, SITE-SPECIFIC SSDNA BINDING-PROTEIN

Estradiol inducible, liver-specific expression of the apoVLDL II gene is mediated through the estrogen receptor and a variety of other DNA-b inding proteins. In the present study we report the cloning and charac terisation of a single-strand DNA binding protein that interacts with the lower strand of a complex regulatory site, which includes the majo r estrogen responsive element and a site that resembles the rat albumi n site D (apoVLDL II site D). Based on its binding specificity determi ned with electro-mobility shift assays, the protein is named single-st rand D-box binding factor (ssDBF). Analysis of the deduced 302 amino a cid sequence revealed that the protein belongs to the heteronuclear ri bonucleoprotein A/B family (hnRNP A/B) and resembles other known eukar yotic single-strand DNA binding proteins. Transient transfection exper iments in a chicken liver cell-line showed that the protein represses estrogen-induced transcription. A protein with similar binding charact eristics is present in liver nuclear extract. The relevance of the occ urrence of this protein to the expression of the apoVLDL II gene is di scussed.