Human β-polymerase gene. Structure of the 5'-flanking region and active promoter

DNA polymerase β (β-pol) is a housekeeping enzyme considered to be involved in DNA repair in vertebrate cells. We cloned a fragment of genomic DNA spanning the first two exons of the human β-pol gene and ~11 kilobases of the flanking region. The segment just 5' of the transcription start site can direct expression of the bacterial chloramphenicol acetyltransferase (CAT) gene in HeLa cells. A sequence containing only 113 base pairs of flanking DNA has promoter activity, and various constructs containing up to 4.8 kilobases of flanking sequence are expressed at a similar level, indicating that with this assay the important regulatory elements are located within or proximal to the ~100-bp core promoter. S1 nuclease mapping was used to show that transcription of the transfected genes is initiated at the same position as the endogenous β-pol gene. The region upstream of the transcription start site is G + C rich and contains neither CAAT nor TATA boxes, but does have three decanucleotide elements matching high affinity binding sites for the RNA polymerase II transcription factor Sp1. Extending 5' from position -39 and surrounded by Sp1 consensus binding elements, there is a 10-nucleotide sequence with perfect dyad symmetry, GTGACGTCAC. Similar sequences are found in a number of cellular and viral promoters, including several adenovirus promoters. Experiments to test whether the core β-pol promoter is activated by the adenovirus early region products showed that cotransfection with an adenovirus expression plasmid strongly activates expression of the β-pol promoter.