Identification and nucleotide sequence of a diversity DNA segment (D) of immunoglobulin heavy-chain genes

Abstract
A putative diversity segment of Ig heavy-chain genes (D segment) was identified 700 base pairs 5'' to JH1 DNA on the germ-line genome of the mouse. This 10-base pair D segment is flanked by 2 sets of sequences which are possible recognition sites for a recombinase. The spacer separating the heptamer and the nonamer is 12 base pairs long on both sides of the D segment. As the spacer separating the 2 signal sequences in VH DNA and JH DNA is 23 .+-. 1 base pairs long, the 2 recombinations required for creation of a complete Ig VH gene, a VH-D joining and a D-JH joining, follow a 12/23-base pair spacer rule. Allelic exclusion is discussed with respect to D segments.