Saturation mutagenesis of a major histocompatibility complex protein domain: Identification of a single conserved amino acid important for allorecognition

The interactive association between T lymphocytes and their target cells is an important system of cell-cell interactions. Major histocompatibility complex class I molecules are the cell surface structures recognized by cytolytic T lymphocytes. To define the molecular structures recognized by cytotoxic T lymphocytes, we have saturated the 270-base-pair α1 exon of the H-2D(p) gene with point mutations, rapidly producing a 'library' of 2.5 x 10³ independent mutants. The library contains enough recombinant clones (each clone encoding approximately one amino acid replacement mutation) to predict a mutation at each nucleotide position of the α1 exon. The functional analysis of the first five transfected gene products tested has shown that mutation of a conserved tyrosine at position 27 to asparagine destroys recognition of the H-2D(p) gene product by polyclonal alloreactive cytotoxic T lymphocytes. Recognition of the same mutant molecule by three monoclonal antibodies and H-2-restricted lymphocytic choriomeningitis virus-specific cytotoxic T lymphocytes is unaffected.