Fig. 2.

Alignment of CSR junctions with germ-line S region sequences. Vertical line indicates direct end-joining, boxes highlight MH, and insertions are underlined. The Sμ, Sα, or Sγ breakpoints are indicated by ▼ or ▲, and positions in germ-line S-region sequences are indicated on top or below the arrowheads. S regions inserted in the reversed direction are designated by (r). Three CSR junctions are shown as examples for different types of end-joining: (A) direct joining; (B) sequential switching from IgM to IgG3, to IgG1, and then to IgG2; and (C) ISD.