Mammalian β-polymerase promoter: Phosphorylation of ATF/CRE-binding protein and regulation of DNA binding

The gene for the mammalian DNA repair enzyme DNA polymerase β (fiβ-pol) is constitutively expressed in most cells, but is regulated in a tissue-specific fashion and can be induced in response to some types of DNA damaging agents. The promoter for the human β-pol gene has been characterized and found to be TATA-less, but it does have multiple GC boxes and one ATF/CRE-bindlng site located within 50 residues 5′ of the major mRNA start site. The ATF/CRE-bindlng site has been found to be essential for activity of the cloned promoter. We report that a bovine testes DNA-binding protein with specificity for the β-pol promoter ATF/CRE-binding site is phosphorylated in vivo and contains several phosphorylation sites. Sequence specific DNA-binding by the purified protein is reduced when the natural protein is dephosphorylated or when it is hyperphosphorylated by protein kinase A (cKA) in vitro. These results suggest the possibility that phosphorylation systems may change binding of this ATF/CRE-blnding protein to the β-pol promoter and in turn modulate the promoter. Possible correlation of the results with transient expression activity of the cloned β-pol promoter fusion gene was obtained in 293 cells. Cotransfection with a cKA expression plasmid to elevate phosphorylation was found to strongly reduce promoter activity.