Component of the signal peptidase complex (SPC) which catalyzes the cleavage of N-terminal signal sequences from nascent proteins as they are translocated into the lumen of the endoplasmic reticulum (PubMed:34388369). Dispensable for SPC enzymatic activity (By similarity). (Microbial infection) Required for the post-translational processing of proteins involved in virion assembly and secretion from flaviviruses such as West Nile virus (WNV), Japanese encephalitis virus (JEV), Dengue virus type 2 (DENV-2), Yellow Fever virus (YFV), Zika virus (ZIKV) and hepatitis C virus (HCV) (PubMed:24009510, PubMed:27383988, PubMed:29593046). Plays a key role in the post-translational processing of flaviviral structural proteins prM, E, and NS1 (PubMed:27383988, PubMed:29593046). In HCV, it is involved in virion assembly where it promotes the interaction between HCV virus proteins NS2 and E2 (PubMed:24009510). Component of the signal peptidase complex paralog A (SPC-A) composed of a catalytic subunit SEC11A and three accessory subunits SPCS1, SPCS2 and SPCS3 (PubMed:34388369). Component of the signal peptidase complex paralog C (SPC-C) composed of a catalytic subunit SEC11C and three accessory subunits SPCS1, SPCS2 and SPCS3 (PubMed:34388369). Within the complex, interacts with SPCS2 and SPCS3 (PubMed:34388369). The complex induces a local thinning of the ER membrane which is used to measure the length of the signal peptide (SP) h-region of protein substrates (PubMed:34388369). This ensures the selectivity of the complex towards h-regions shorter than 18-20 amino acids (PubMed:34388369). (Microbial infection) Interacts with hepatitis C virus (HCV) proteins NS2 and E2 (PubMed:24009510). Interacts with NS2B from Japanese encephalitis virus (JEV), West Nile virus (WNV), and Zika virus (ZIKV) (PubMed:29593046). May be phosphorylated. Belongs to the SPCS1 family. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus.