Tapasin may also have a role in stablising "empty" MHC class 1 molecules (i.e. those without peptides destined for presentation), epitope selection and quality control after peptide binding.
References
^Daumke, O. (2001) Functional asymmetry of the ATP-binding-cassettes of the ABC transporter TAP is determined by intrinsic properties of the nucleotide binding domains. Eur. J. Biochem., 268:4776-4786.
^Suh, WK. (1994) Interaction of MHC class I molecules with the transporter associated with antigen processing. Science. Vol 264 5163:1322-1326.