I‐J expression is not associated with murine chromosome 4

I‐J originally mapped within the murine major histocompatibility complex (H‐2) between the E_B and E_a, loci using intra‐H‐2 recombinants. Cloning of this segment of H‐2 shows no DNA that can be ascribed to I‐J. Various hypotheses have attempted to explain this dilemma. One hypothesis attributes a chromosome 4 locus with I‐J^k expression. This hypothesis requires the AKR/J and A/WySn mouse strains to be I‐J^k negative. In the present report we show that AKR/J spleen cells express I‐J^k surface molecules and that both the AKR/J and A/WySn mouse strains produce functional I‐J^k‐bearing suppressor factors to poly(Glu⁵⁰Tyr⁵⁰). Our data imply that mapping of I‐J‐determining genes to chromosome 4 may be premature.