Duplicated copies of the bovine JH locus contribute to the Ig repertoire

We report the cloning and analysis of a bovine J(H) locus comprising a DQ52 segment, six J(H) segments and sequence to a 5' H chain intronic enhancer. The contig was mapped to BTA 11 and evidence was found for rearrangement of the sixth J(H) segment at a low but detectable frequency. In contrast, the fourth segment present at a second copy of the bovine J(H) locus mapping to BTA 21 was found to rearrange at high-frequency, forming FR4 in the majority of bovine Ig H chains. The data thus show that bovine H chains can be generated from segments at two distinct genomic locations. Further investigation should establish if rearrangement takes place at each locus or if the participating segments are brought together from different chromosomal locations by less conventional processes (for example by gene conversion or trans-chromosomal rearrangement).