Signal Sequence Receptor Beta (SSRb)

In order to translocate membrane or secretory proteins across the endoplasmic reticulum (ER) membrane, the signal sequence of a nascent peptide is recognized by a signal recognition particle (SRP), by which the nascent peptide associated with a ribosome can bind to the ER membrane receptor (or docking protein). SRP is released from both the ribosome and the signal sequence; the latter lies near an integral, glycosylated ER membrane protein referred to as the signal sequence receptor (SSR). The SSR consists of 2 subunits, a 34-kD glycoprotein (alpha-SSR or SSR1) and a 22-kD glycoprotein (beta-SSR or SSR2). Northern blot analysis revealed its ubiquitous expression in all organs examined. By fluorescence in situ hybridization, they localized the human beta-signal sequence receptor gene (SSR2) to chromosome bands 1q21-q23.