Linkage of variable and joining gene segments in the murine immunoglobulin kappa locus

We have previously isolated a series yeast artificial chromosome (YAC) clones which span the murine immunoglobulin kappa locus of mouse [PNAS 92, 12421 (1995)]. Our results indicate that Igκ is one of the largest immunoglobulin loci described to date, spanning more than 3.0 Mb. Despite its exceptional size, Igκ undergoes precise patterns of developmental activation. Thus far, two enhancers have been identified in Igκ both residing at the 3′ end of the locus. The extreme distance of these enhancers from the distal variable (Vκ) gene segments raises the interesting question of whether they are sufficient for locus regulation. In order to address this issue, we have selected to study other regions which may contain new regulatory elements. One of these regions is the intervening region between the joining (Jκ) gene segments and the most proximal variable (Vκ) gene segment. Using a reverse genetic technique in yeast (chromosome fragmentation) we have mapped the proximal Vκ gene segment (Vκ21G) relative to the constant region. Using long PCR we have confirmed this observation and measured the distance to be 21 kb. We are currently sequencing this region and analyzing it for the presence of tissue specific DNase I hypersensitive sites.