Required for protein translocation and folding in the endoplasmic reticulum (ER). Functions as a nucleotide exchange factor for the ER lumenal chaperone HSPA5. Interacts with HSPA5. N-glycosylated. Ubiquitinated by the CRL2(FEM1A) and CRL2(FEM1C) complexes, which recognize the -Lys-Xaa-Xaa-Arg C-degron at the C-terminus, leading to its degradation. Belongs to the SIL1 family.