Abstract: The invention provides for novel noxin polypeptides and nucleic acids from humans, rats, and mice and to related compositions and uses. The invention also provides for the creation of non-human, transgenic mammals which have, incorporated in their genome, DNA that includes a sequence of a mammalian noxin gene that does not produce noxin polypeptides, i.e. a noxin knockout mouse. The invention also provides for methods for protecting a cell from stress damage by enhancing the expression noxin, methods for decreasing cell death by enhancing the expression of noxin, methods for inducing cell death by decreasing noxin activity, methods for inducing cell cycle arrest by increasing noxin, and methods for preventing cell cycle arrest by inhibiting noxin activity.