MA5.8 cells transduced with patient mutant CD3ζ cDNA do not express detectable CD3ζ protein and fail to assemble complete TCR complexes. MA5.8 hybridoma cells retrovirally transduced with the indicated human CD3ζ cDNAs or pMiG vector alone were metabolically labeled for 30 minutes and lysed in digitonin lysis buffer. Lysates were either sequentially immunoprecipitated with anti-CD3ε Ab followed by anti-CD3ζ Ab or immunoprecipitated with anti-CD3ζ Ab alone. Immunoprecipitated material was resolved by SDS-PAGE and TCR chains visualized by fluorography.