At a multiplicity of infection (moi) of 600 Ad-Per2 restored paraquat induced cytotoxicity in Per2Brdm1 mutant cells from 37.7 ± 2 (% cytotoxicity ± SEM) to 45.5 ± 3.1%, a level comparable to wild-type cells (43.9 ± 1.3%) (Table 1). Here, PER2 is linked to infection.