SUMMARY PARAGRAPH for SPC2
SPC2 encodes a subunit of the signal peptidase complex (SPC), which cleaves the signal sequence from proteins targeted to the endoplasmic reticulum (ER) (1). Signal peptide cleavage occurs concomitantly with translocation through the translocon pore into the ER. In yeast, translocation can occur cotranslationally or posttranslationally, whereas in mammals translocation is always cotranslational. The process of protein translocation into the ER is reviewed in references 5 and 6.
The yeast SPC comprises four proteins, Spc1p, Spc2p, Spc3p, and Sec11p (7, 4). Spc2p is homologous to the mammalian signal peptidase subunit SPC25 (1). Spc2p is not essential for viability or for signal peptidase activity (1, 4), but deletion of SPC2 reduces signal peptidase activity in vitro (4). The spc2 null mutant also shows reduced levels of the other SPC subunits (4), and is synthetically lethal with a temperature-sensitive mutation in SEC11 (1).
Spc2p can be coimmunoprecipitated with Sbh1p and Sbh2p, which are beta subunits of two different "Sec61" complexes involved in ER membrane translocation (4, 6). The genetic and physical interactions observed suggest that Spc2p may facilitate interactions between different components of the translocation machinery (4).
Last updated: 2000-11-28