π, a Pre-B-Cell-Specific Enhancer Element in the Immunoglobulin Heavy-Chain Enhancer

We have identified a new immunoglobulin heavy-chain enhancer element, designated π, between the µE2 and µE3 elements. The π enhancer element is transcriptionally active primarily during early stages of B-cell development but becomes virtually inactive during B-cell maturation at about the stage of immunoglobulin K light-chain gene rearrangement. Mutational analysis suggests that the π element is crucial for immunoglobulin heavy-chain enhancer activity at the pre-B-cell stage but is almost irrelevant for enhancer activity at the mature B-cell or plasma-cell stage. The activity of the π enhancer element correlates with the presence of an apparently pre-B-cell-specific protein-DNA complex. The similarity of the π site to recognition sequences for members of the ets gene family suggests that the protein(s) interacting with the π site most likely are ets-related transcription factors.