However, xeroderma pigmentosum (XP) group variant (XP-V) cells, in which Polη is inactivated (Johnson et al, 1999; Masutani et al, 1999), are not sensitive to illudin S, suggesting that Polη is not involved in bypassing illudin S–induced DNA lesions (Jaspers et al, 2002). The gene discussed is POLH; the disease is xeroderma pigmentosum.