Activation of V kappa gene rearrangement in pre‐B cells follows the expression of membrane‐bound immunoglobulin heavy chains.

During B cell development V kappa gene rearrangement seems to occur only in mu‐positive pre‐B cells. To study the role of the mu chain in the activation of the Ig kappa locus, we introduced expression vectors carrying different forms of the mu gene into null pre‐B cells. The activation of the Ig kappa locus followed the expression of the membrane form (micron) of the mu chain. The expression of the secreted form (microS) did not result in the activation of the Ig kappa locus. We further show that both forms of the mu chain differ in their intracellular transport in pre‐B cells.