||PAX5 encodes a member of the paired box (PAX) family of transcription factors. The central feature of PAX5 family is a novel, highly conserved DNA-binding motif, known as the paired box. Paired box transcription factors are important regulators in early development, and alterations in the expression of PAX5 are thought to contribute to neoplastic transformation. PAX5 encodes the B-cell lineage specific activator protein that is expressed at early, but not late stages of B-cell differentiation. Its expression has also been detected in developing CNS and testis and so the paired box 5 may also play a role in neural development and spermatogenesis. PAX5 is located at 9p13, which is involved in t(9;14)(p13;q32) translocations recurring in small lymphocytic lymphomas of the plasmacytoid subtype, and in derived large-cell lymphomas. This translocation brings the potent E-mu enhancer of the IgH gene into close proximity of the PAX5 promoter, suggesting that the deregulation of transcription of PAX5 contributes to the pathogenesis of these lymphomas. Alternative splicing results in multiple transcript variants encoding different isoforms.