A negative regulatory element in the rabbit 3'IgH chromosomal region.

Mouse and human IgH loci contain several 3'IgH enhancers. In rabbit, a single hs1,2 enhancer is located 3' of the distal germ line Calpha gene, Calpha13. We searched for additional regulatory elements in this region by using a luciferase reporter assay and nucleotide sequence analysis. Within 8 kb 3' of Calpha13, we identified a 1-kb fragment that negatively regulated the hs1,2 enhancement of the Ialpha promoter. This negative regulatory element, Calpha-NRE, contains a conserved 300-bp region that is associated with 8 of the 13 germ line Calpha genes. This conserved region contains an E box that, by electrophoretic mobility shift assay, binds an E47-like protein. At the 5' end, Calpha-NRE also includes a 270-bp region with 20-bp repeats nearly identical to those 3' of mouse and human Calpha genes, and these repeats bind unidentified nuclear protein(s). Calpha-NRE appears to be a novel regulatory element that may contribute to the regulation of IgH gene expression.