Samui, a novel cold-inducible gene, encoding a protein with a BAG domain similar to silencer of death domains (SODD/BAG-4), isolated from Bombyx diapause eggs

Cellular responses to cold-acclimation have not yet been studied in depth. To explore this field, we focussed on insect diapause development. Although embryonic diapause of Bombyx mori is sustained at 25 degreesC, chilling at 5 degreesC for 2 months causes diapause termination, a transition that is marked when the sorbitol dehydrogenase gene (SDH) is activated. To clarify the relationship between this activation and incubation at 5 degreesC, we i solated a novel cold-inducible gene, Samui. Expression of Samui mRNA and pr otein was activated after incubation at 5 degreesC for 5-6 days, lasted for another 30 days and then weakened. Exposure to 25 degreesC suppressed both mRNA and protein expression. In nondiapause eggs incubated at 5 degreesC, Samui was also up-regulated, although the expression was weaker. Samui cont ained nuclear localization-signals, a ssDNA-binding motif and a BAG domain similar to that of SODD/BAG-4. Because Samui could bind to HSP70, it is a m ember of BAG protein family. It is proposed that Samui serves to transmit t he '5 degreesC signal' for SDH expression in diapause eggs, while also prot ecting against cold-injures in nondiapause eggs, through binding to respect ive partners. This is the first report that a member of BAG protein family is up-regulated by cold.