In RLGS-M (restriction landmark genomic scanning using methylation-sensitive endonuclease) displays of mouse brains, spot #91 is one of tissue-specific gel spots whose intensity changes developmentally. We have now cloned the corresponding cDNA from this spot and analyzed its structure and expression. The deduced amino acid sequence revealed that the #91 cDNA encodes a novel protein of 403 amino acids which consists of a cysteine-rich domain and a SH3 domain. We designated this gene as Stac. Northern blotting and in situ hybridization analyses demonstrated that 2.7 kb of Stac mRNA is expressed predominantly in brain and neurons, especially in hippocampus, cerebellum and inferior olive. Further, the gene product of 47 kDa was found by western blotting analysis in the soluble fractions of brain as well as Stac-expression vector-transfected NIH3T3 cells. Although the function of Stac is unknown so far, it is likely involved in a neuron-specific signal transduction.