Maternally transmitted antigen of mice: a model transplantation antigen.

Molecular identification proved Mta, the maternally transmitted antigen of mice, to be a model minor histocompatibility (H) antigen. It consists of a peptide, MTF, that is presented on the cell surface by an H-2 class-I molecule, HMT. MTF is derived from ND1, a mitochondrially encoded protein, and the amino-terminal N-formyl-methionine is essential for binding to HMT; conservative substitutions at the sixth residue causes MTF to be a minor H antigen. HMT is encoded by the M3 gene at the telomeric end of the H-2 complex. The peptide-binding site of HMT is hydrophobic, and allelic forms of the mature protein differ by only three amino acids. Homologues and analogues of the mouse Mta system have recently been identified in rats.