Beschreibung:
<jats:p>Using extracts of AtT‐20 cell nuclei, protein binding sites on the POMC gene 5'‐flanking region were examined with an exonuclease protection approach. One such binding site, located from −119 to −106 bp upstream from the mouse POMC gene transcription initiation site, which exhibited a close homology to the aetivator protein‐2 (AP‐2) site [1]. A double‐stranded oligonucleotide containing this site was subsequently used in gel shift assays to demonstrate AP‐2 consensus sequence binding activity in extracts of AtT‐20 cell nuclei. Gel shift competition experiments using both homologous and heterologous competitor DNA sequences revealed that the AP‐2 like factor(s) exhibited specific binding to the mouse AP‐2 consensus sequence. Furthermore, AP‐2 factor binding was also modulated by a CTF/NFl‐like factor. Pretreatment of AtT‐20 cell nuclear extracts with alkaline phosphatase prior to inclusion in gel shift assays led to a reduction in the intensities of AP‐2 factor‐specific bands, indicating a potential involvement of protein phosphorylation in AP‐2 factor binding in AtT‐20 cells.</jats:p>