Cells of encysted gastrula embryos of the crustacean Artemia franciscana exhibit extraordinary stability during prolonged anoxia. We find that they contain an abundant protein (referred to as "26-kDa protein") that undergoes translocation to the nucleus during anoxia. The reverse translocation rapidly occurs when anoxic embryos are returned to aerobic conditions. A similar translocation appears to take place in embryos exposed to 42 degrees C aerobic heat shock and prolonged exposure to low temperature (0-2 degrees C), and in diapause embryos. Gel filtration and Western immunoblotting indicate that the 26-kDa protein is translocated to other cellular compartments and may also be associated with a wide variety of "soluble" proteins during anoxia. This protein makes up roughly 15% of the total nonyolk embryo protein and is, by far, most abundant in the encysted embryo stage of the life cycle. The hypothesis is advanced that the 26-kDa protein may play the role of a metabolic regulator and/or a protective molecular chaperone during prolonged anoxia and other forms of stress.