Generation and expression of 2B4 deletion mutants. HA-tagged deletion mutants of 2B4 containing no (D0), 1 (D1), 2 (D2), 3 (D3), or a mutated third (Y3F) ITSM (black boxes) were generated by inserting a stop codon or a point mutation at different positions in the 2B4 cytoplasmic tail. Mutants were expressed in the NK cell line YTS by retroviral gene transfer. Expression was monitored by staining transduced cells with a control antibody (open curve) or an anti-HA antibody (filled curve). TM indicates transmembrane domain.