In this thesis, I sought to identify novel components of the "peptide loading complex" (PLC) that is involved in delivering peptide ligands to major histocompatibility complex (MHC) class I molecules. An anti-tapasin affinity column was used for the large-scale isolation of the PLC from EL4 cell microsomes. The isolated PLC was separated on an SDS-PAGE gel and protein components were visualized with silver staining. Proteins of interest were processed for tandem mass spectrometry analysis. GenBank database searching with information obtained from the mass spectrometry analysis revealed three novel components, heat shock cognate protein 70 (Hsc70), ribophorin I and oligosaccharide transferase 48 (OST48). Their presence in the PLC was confirmed by Western blot, suggesting a physical link between protein degradation pathways and the PLC. Based on the findings I discussed how such a link may ensure efficient generation of MHC class I:peptide complexes for T cell surveillance.