ULTRAVIOLET-INDUCED CELL-DEATH BLOCKED BY A SELENOPROTEIN FROM A HUMAN DERMATOTROPIC POXVIRUS

Selenium, an essential trace element, is a component of prokaryotic an d eukaryotic antioxidant proteins, A candidate selenoprotein homologou s to glutathione peroxidase was deduced from the sequence of molluscum contagiosum, a poxvirus that causes persistent skin neoplasms in chil dren and acquired immunodeficiency syndrome (AIDS) patients. Selenium was incorporated into this protein during biosynthesis, and a characte ristic stem-loop structure near the end of the messenger RNA was requi red for alternative selenocysteine decoding of a potential UGA stop co don within the open reading frame. The selenoprotein protected human k eratinocytes against cytotoxic effects of ultraviolet irradiation and hydrogen peroxide, providing a mechanism for a virus to defend itself against environmental stress.