REQUIREMENT OF MAMMALIAN DNA POLYMERASE-BETA IN BASE-EXCISION REPAIR

SYNTHESIS Of DNA by DNA polymerase-beta is distributive on single-stra nded DNA templates, but short DNA gaps with a 5' PO4 in the gap are fi lled processively to completion(1,2). In vitro studies have suggested a role of beta-polymerase in different types of DNA repair(3-9). Howev er, the significance of these studies to the in vivo role of beta-poly merase has remained unclear. Because genetic studies are essential for determining the physiological role of a gene, we established embryoni c fibroblast cell lines homozygous for a deletion mutation in the gene encoding DNA polymerase-beta. Extracts from these cell lines were fou nd to be defective in uracil-initiated base-excision repair. The beta- polymerase-deleted cells are normal in viability and growth characteri stics, although they exhibit increased sensitivity to monofunctional D NA-alkylating agents, but not to other DNA-damaging agents. Both the d eficiency in base-excision repair and hypersensitivity to DNA-alkylati ng agents are rescued following stable transfection with a wild-type b eta-polymerase minitransgene. These studies demonstrate that beta-poly merase functions specifically in base-excision repair in vivo.