Immunoglobulin J (IgJ)

J chain is a 137-amino acid protein that is synthesized in B lymphocytes and serves 2 known functions: linking immunoglobulin monomers (IgM to pentamers, IgA to dimers) and binding these immunoglobulins to secretory component (Koshland, 1985). Using probes from J chain clones, Max et al. (1986) assigned the J chain gene to 4q21 by Southern analysis of somatic cell hybrids and by in situ hybridization. This band is the site of translocations with chromosome 11 in some acute lymphocytic leukemias. In the mouse, JCH maps to chromosome 5 which carries 4 other genes that are also on human no. 4 (PGM2, PEPS, ALB, and AFP). Max et al. (1986) also discovered genetic variation in the number of repeats of a 27-bp sequence that is tandemly reduplicated 5-prime of the human J chain gene.