Map of the human VH6-DJ-Cμ locus. Shown is a 400-kb region extending from V_H6 through Cμ. The approximate positions of the DXP gene segments are denoted within each of the four D_H tandem repeats in the distal D_H locus, labeled as DXP1 (D21/7) and DXP1′ (D21/0.5), DXP2, DXP3, and DXP4. The expanded portion indicates the location of D_HQ52 within the proximal D_H locus, the six J_H gene segments, and the intronic sequence between J_H and Cμ that includes the proximal IgH enhancer. The composition of germline transcripts from D_HQ52, Iμ, and germline Cμ is illustrated. For the transcripts shown, boxes indicate transcribed regions and lines indicated areas that are removed due to RNA processing.