To further our understanding of the role of stress proteins in development as well as in adaptation of fish to adverse environmental conditions, we undertook molecular analyses of stress protein encoding genes from the hermaphroditic teleost Rivulus marmoratus. We isolated a genomic clone containing the Hsc71 gene (rm-hsc71m) and its upstream sequences. rm-Hsc71m is not induced by external stress, but is enriched in a tissue-specific manner during early development. In adult, the strongest expression appeared in skeletal muscle, whereas lower expression was seen in the gill, eye and brain. To understand the regulatory basis of high muscle expression of rm-hsc71m, transfection of R.marmoratus muscle tissue was performed using 5' deletion fragments containing the rm-hsc71m promoter driving EGFP expression. An upstream region from -2.7 to -1.9 kb was identified as a muscle-specific regulatory region. Within this region, we identified at least three sites with the novel sequence TGTnACA interacting with a fish muscle factor having an M(r) of 32 000. Our data indicate that rm-hsc71m expression in skeletal muscle is controlled by a muscle-specific regulatory element containing this novel motif.