Polymorphic mutations in the polb gene promoter and their impact on transcriptional activity

Background DNA polymerase beta is one of the key enzymes involved in DNA damage repair and its proper expression is strictly controlled within different cells. We previously reported that three genetic mutations in the promoter region of the polb gene are prevalent in the Chinese Han population and two types of mutation are associated with thymic hyperplasia. The purpose of this study was to explore whether other mutated sites exist within the promoter region of the polb gene. Methods Genomic DNAs of 421 healthy Chinese Han individuals were extracted from whole blood samples and used for gene amplification of the promoter region of the polb gene. After gel purification, PCR amplicons were sequenced by the Sanger sequencing method and used for sequence alignment with the Lasergene program. PCR products with novel mutations were then subcloned into luciferase reporter plasmid pGL4.10 and transfected into 293T cells for dual-luciferase activity analysis. Results In total, 11 mutated sites were detected in the Chinese Han population and eight of these were reported for the first time. Using a dual luciferase reporter system, it was found that one novel mutation -142 C > G could decrease the transcription activity of the polb gene, whereas two novel mutations, -152_-151insC and -218 C > G, could significantly increase the transcription activity of the polb gene. Conclusions High polymorphic sites could be found in the promoter region of polb gene and approximately half of them could influence its transcription activity.