Pax‐5 is identical to EBB‐1/KLP and binds to the VpreB and λ5 promoters as well as the KI and KII sites upstream of the Jχ genes

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Abstract
During B cell differentiation, the pre‐B cell stage plays a significant role in immunoglobulin gene rearrangement in the context of the allelic exclusion and χ chain gene rearrangement. We previously reported that the early B cell‐specific binding protein (EBB)‐1 transcription factor binds to the promoters of two pre‐B cell‐specific genes, VpreB and λ5, and regulates their pre‐B cell‐specific expression. Here, we demonstrate that EBB‐1 binds to the KI and KII sites in the upstream of Jχ region, which are crucial for χ chain gene rearrangement. Gene transfer and gel‐shift assays demonstrate that EBB‐1 is identical to Pax‐5 and binds to promoters of VpreB and λ5 as well as the KI and KII sites. Our results suggest that Pax‐5 plays an important role in the coordinate regulation of several immunoglobulin gene family members that are crucial in B cell development.