Immunoglobulin Heavy Chain Switch Regions

Alternatively, c-myc may itself be a target for factors that promote class switch recombination in activated B cells. Like the immunoglobulin heavy chain switch regions, c-myc is rapidly transcribed in activated B cells, and the first exon and intron of c-myc, where translocation junctions map, contains numerous G-runs with potential for formation of G-quadruplexes. 

The p-constant region segment is a component of all newly rearranged immunoglobulin genes, but later in the life span of the cell, there is yet another recombination event called heavy-chain switching in which the p chain is deleted and a g chain is joined to the same V-D-J segment. The p- and (d-) chain antibodies are membrane-bound, whereas the g-chain antibodies (as well as other heavy-chain antibodies) are secreted by the cell. 

Figure 6 Immunoglobulin heavy chain class switch recombination. (A) The murine heavy chain locus is shown before and after recombination from g. to yl, which results in expression of IgGl antibodies. Deleted sequences can be recovered in circular DNA molecules from B cells which have recently completed switch recombination. V, variable region C, constant region and S, switch region. (B) Examples of consensus G-rich repeats from some murine S regions...

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