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figure 6

Figure 6 - Class switch IgM-IgG1: Smu-Sgamma1 recombination

In a B cell which expresses IgM on the cell surface, a productive rearranged IGHV-D-J gene on one chromosome 14 is transcribed with the IGHM gene. Before the switch recombination, all the IGHC genes are present in the IGH locus. During the switch recombination, a novel DNA rearrangement occurs in the IGH locus, between the Smu (Switch mu) sequence and another S sequence located in 5' of a more downstream IGHC gene (for example, Sgamma1 upstream of IGHG1). This leads to the deletion of the intermediary DNA and to the loss of the IGHC genes located between the two S sequences which recombine. The enhancer (E5') located between the most 3' IGHJ and Smu is retained during the switch recombination.