Signal sequence receptor subunit delta (SSR4, or TRAPD) gene encodes the translocon-associated proteins subunit delta, which is about 19- kDa and is located at endoplasmic reticulum (ER) membrane, the translocon-associated proteins complex functions to bind calcium to the ER membrane and thereby regulate the retention of ER resident proteins. TRAP-delta can form heterotetramer with other TRAP homolog TRAP-alpha, TRAP-beta and TRAP-gamma.