Deinococcus radiodurans and other species of this genus share extreme resistance to ionizing radiation and many other agents that damage DNA. D. radiodurans mutant strains defective in a deinococcal DNA polymerase that is homologous with E. coli DNA polymerase I are highly sensitive to DNA damage. In the current work we have inquired whether E. coli DNA Pol I can substitute for D. radiodurans Pol in partially or fully restoring to pol- D. radiodurans mutants the extreme DNA damage-resistance typical of this organism. The E. coli polA gene or a 5'-truncated polA gene that encodes the Klenow fragment were introduced and expressed in two different D. radiodurans pol- mutants: Strain 303, which is a chemically mutagenized derivative, and strain 6R1A, which is isogenic with wild-type D. radiodurans except for an insertional mutation within the pol gene. Expression of E. coli polA in both of these mutants fully restored wild-type resistance to ionizing- and UV254-radiation and mitomycin-C exposure. Expression of the Klenow fragment-encoding gene restored wild-type resistance to D. radiodurans strain 303, but only partial resistance to strain 6R1A. The observation that E. coli DNA Pol I is as effective as D. radiodurans Pol in restoring damage resistance, indicates that D. radiodurans DNA Pol per se does not have special properties that are essential or prerequisite for expression of the extreme resistance of D. radiodurans.