DNA polymerase X from Deinococcus radiodurans implicated in bacterial tolerance to DNA damage is characterized as a short patch base excision repair polymerase

Abstract

TheDeinococcus radioduransR1 genome encodes an X-family DNA repair polymerase homologous to eukaryotic DNA polymeraseβ. The recombinant deinococcal polymerase X (PolX) purified from transgenicEscherichia colishowed deoxynucleotidyltransferase activity. Unlike the Klenow fragment ofE. coli, this enzyme showed short patch DNA synthesis activity on heteropolymeric DNA substrate. The recombinant enzyme showed 5′-deoxyribose phosphate (5′-dRP) lyase activity and base excision repair functionin vitro,with the help of externally supplied glycosylase and AP endonuclease functions. ApolXdisruption mutant ofD. radioduransexpressing 5′-dRP lyase and a truncated polymerase domain was comparatively less sensitive toγ-radiation than apolXdeletion mutant. Both mutants showed higher sensitivity to hydrogen peroxide. Excision repair mutants ofE. coliexpressing this polymerase showed functional complementation of UV sensitivity. These results suggest the involvement of deinococcal polymerase X in DNA-damage tolerance ofD. radiodurans, possibly by contributing to DNA double-strand break repair and base excision repair.