DNA polymerase beta (pol beta) is a constitutively expressed DNA repair enzyme in vertebrate cells. Yet, it had been shown previously that the pol beta mRNA level increases in Chinese hamster ovary (CHO) cells within 4 h after treatment with several monofunctional DNA damaging agents, notably, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Herein we report that a transfected pol beta promoter fusion gene is activated by MNNG treatment of CHO cells; mRNA from the transfected gene is approximately 10-fold higher in treated cells than in untreated cells 16 h after treatment. This activation is mediated through the decanucleotide palindromic element GTGACGTCAC at positions -49 to -40 in the "TATA-less" core promoter. This element, which is similar to the ATF/CREB transcription factor-binding site in a number of mammalian genes, forms the center of a strong protein-binding site for CHO cell nuclear extract proteins. Mutated pol beta promoter fusion genes lacking the element fail to bind protein at this site and fail to respond to MNNG treatment of cells.