Immunoglobulin biosynthesis in mouse thymus cells. The expression of α and μ chains in BALB/c, C57BL and intercrossed hybrid mice

C57BL thymocytes synthesize preferentially μ-heavy chains, in constrast to the BALB/c thymocytes which produce mainly α chains. In thymocytes obtained from F₁ hybrids and their backcrosses to BALB/c and C57BL mice, both α and μ chains were synthesized. However, distinct differences were found in the relative amount of nascent α and μ chains among the various crosses and the observed amount of μ-chain synthesis in the hybrids thymocytes was significantly lower than that expected according to simple mendelian modes of inheritance. We therefore assume that the expression of either of the genes which control α- or μ-chain synthesis is regulated by an additional gene, whose presence or absence will determine the relative quantities of α and μ chains produced in any of the strains.