STAC is a 402 amino acid protein that contains one SH3 (Src homology 3) domain and one cysteine-rich domain (CRD). Expressed in brain, STAC is a neuron-specific protein that localizes to the cytoplasm and, based on the frequent involvement of SH3 and CRD domains in signal transduction, is believed to play a role in neuron-specific signal transduction. In addition, STAC may be involved in protecting cells from apoptosis. Due to its neuron-specific expression and putative role in signal transduction, STAC may be implicated in a variety of hereditary neurological diseases.