Induction of lambda 1-immunoglobulin is determined by a regulatory gene (r lambda 1) linked (or identical) to the structural (c lambda 1) gene.

The cis-acting gene regulating specifically the inducibility of lambda 1-bearing B cells has been mapped within 2.9 cM of the structural gene. If the lambda 1lo-phenotype is due to the gly leads to val interchange in C lambda 1, then an argument can be made that (a) the lambda 1lo-phenotype is due to inefficient induction of lambda 1lo-bearing B cells and (b) B cell triggering is dependent upon a conformational change in the Ig receptor upon interaction with antigen. If the lambda 1lo-phenotype is due to a regulatory sequence linked to the structural C lambda 1-gene, then it must control the expression of the lambda 1-locus during development into adulthood, e.g., by an effect on methylation.