Deletions in the constant region locus can account for switches in immunoglobulin heavy chain expression.

Deletions spanning portions of the heavy chain constant region (CH) locus in murine plasmacytomas are revealed by hybridization with cloned immunoglobulin DNA molecules. The pattern of deletions suggests that a lymphocyte clone switches expression of CH genes by successive deletions and that the probable CH gene order is 5' mu-gamma 3-gamma 1-gamma 2b-gamma 2a-alpha 3'.