The function of SPCS1 (signal peptidase complex subunit 1, Ensembl gene identifier ENSG00000114902) is as follows. 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). {ECO:0000250|UniProtKB:P46965, ECO:0000269|PubMed:34388369}. (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). {ECO:0000269|PubMed:24009510, ECO:0000269|PubMed:27383988, ECO:0000269|PubMed:29593046}.