Human natural killer cells and mature T lymphocytes express identical CD3ζ subunits as defined by cDNA cloning and sequence analysis

In order to characterize the CD3 ζ‐related protein found in human natural killer (NK) cells and compare it with CD3 ζ expressed in T lymphocytes, the present study was performed. A polyclonal CD3⁻CD16⁺NK population displaying a strong non‐major histocompatibility complex‐restricted cytotoxic activity against the NK target K‐562 was isolated and a product corresponding to CD3 ζ amplified using the polymerase chain reaction method. This 0.6‐kb product was present in similar amounts in NK cells and T cells. In contrast, a product corresponding to CD3 ζ was amplified from T lymphocytes exclusively. Thus, the CD3 ζ product detected in NK cells did not originate from contaminating T cells. DNA sequence analysis of two independent polymerase chain reaction products from the NK cells demonstrates that human NK cells and mature T cells share a CD3 ζ subunit with an identical primary amino acid sequence. The nucleotide sequence of a third NK‐derived cDNA revealed an insertion of a CAG triplet encoding an additional glutamine residue in the cytoplasmic domain. Since this residue is encoded by nucleotides at a putative RNA splice junction, it possibly results from a difference in pre‐mRNA splicing. Taken together, these data show that CD3 ζ is not structurally distinct in NK cells and in T lymphocytes.