The structure of the rearranged IgH in sorted late pro-B cells from 24-day-old Eμ-ret (Tg+) and transgene-negative (Tg−) mice. Twenty-five and 36 unique VDJ joinings were PCR-amplified from DNA obtained from the bone marrow of Tg− and Tg+ mice, respectively. In the upper graph, N regions are defined as nontemplate derived nucleotides that are found at the VD or DJ junction. In the lower graphs, V and D gene family and J gene usage within the VDJ joinings was assigned as detailed in Materials and Methods.