The bovine DNA polymerase β promoter: cloning, characterization and comparison with the human core promoter

The core promoter of the human DNA polymerase β (βPol)-encoding gene (POLβ) is regulated through cis-elements for the ATF/CREB protein(s), and GC box-binding and initiation-site-binding proteins. The mechanism of promoter regulation has been studied using a nuclear extract transcription system from HeLa cells [Narayan et al., J. Biol. Chem. 269 (1994) 12755-12763]. To study the homologous promoter (ppolβ) in a bovine system, we cloned and characterized the 5′-flanking region of the bovine gene (polβ). A 15.3-kb fragment of bovine genomic DNA containing the first two exons and 11 kb of 5′-flanking region was isolated from a testis library in bacteriophage λEMBL3. S1 nuclease mapping and primer extension analysis of the 5′-end of the polβ mRNA identified the major transcription start point (tsp), which is located 142-bp 5′ of the translational start codon. In transient expression assays using a bovine cell line, analysis of various 5′-deletion mutants demonstrated that a fragment of only 91-bp 5′ of the tsp had promoter activity similar to that of a 1.37-kb fragment, so that cis-elements for basal transcription are located within this approx. 100-bp core promoter, as in the human promoter (pPOLβ). Comparison of the core promoters from the bovine and human genes revealed striking similarity, including an almost precise match of the tsp, the ATF/CREB-binding and Spl-binding sites, and the spacing separating them.