Abstract
Pyrococccus horikoshii OT3 (OT3) is the anaerobic hyperthermophilic archaeon, whose genome analysis has been completed. Instead of normal SOD/catalase system, this strain possesses unusual scavenging system for O2−and H2O2 due to Superoxide reductase/ Peroxideredoxin, in which O2 is not generated as a byproduct. Thymine glycol (Tg) is a well-known oxidative base lesion, which blocks DNA replication. The endonuclease III (Nth) has been isolated and characterized from various aerobes as a repair enzyme for Tg. To understand repair mechanism for oxidative base lesions in OT3, we search homologues in the database, and found a candidate for Nth homologue. To clarify whether this candidate is functional, we cloned the gene, purified OT3-Nth, and measured the enzymatic activity by using nicking assay with dsDNAs containing various oxidative lesions including Tg. The OT3-Nth was able to release these lesions by glycosylase activity and also cleave backbone producing 3'-OH at AP site by AP lyase activity. These results strongly suggest that OT3-Nth is the Nth homologue in Pyrococccus horikoshii OT3. [J Radiat Res 44:422 (2003)]
