Switch junction analysis in 6 MM patients. Homologies between switch regions and the switch junction sequence were determined by BLAST and ClustalW analysis. Switch junctions are indicated with open boxes. Upper sequence indicates Sμ switch region; center, switch junction sequence from this study; and lower, Sγ switch region. Switch base positions are shown in bold. Vertical lines indicate sequence identity; dashes, spaces introduced for optimal alignment. A switch junction microhomology of 4 to 5 bp is evident in patient MM1.