In mammalian cells, hydrogen peroxide is known to induce the expression of several genes thought to be important in protection against oxidative stress. Using mRNA differential display, we have identified a novel RNA in hamster HA1 cells that is strongly induced by hydrogen peroxide under conditions where a protective adaptive response occurs. This induction was observed between 1 and 18 h after peroxide treatment, and at an H2O2 concentration that caused little or no cytotoxicity. Northern blot analysis revealed that this major inducible RNA species, termed adapt15 is 950 bases in size. Two versions of this RNA were found by sequence analysis, differing only by a short trinucleotide stretch. Despite polyadenylation, no large open reading frame was observed. Fractionation studies, however, indicate that adapt15 RNA is primarily located in the cytoplasm, and a signicificant percentage of it is associated with active translation. adapt15 RNA may act at the level of translation to protect cells against the damaging effects of oxidative stress. (C) 1996 Academic Press, Inc.