Provides significant protection from radiation damage and may be involved in the degradation of radiation-damaged nucleotides. Toroid-shaped homohexamer. In the hexamer, 3 dimers assemble to form a ring-like structure surrounding a central hole. Cells lacking this gene show a 2-3 orders of magnitude drop in survival after exposure to ionizing radiation as compared to a wild-type strain. Belongs to the GTP cyclohydrolase I type 2/NIF3 family.