該基因編碼轉錄因子成對盒（PAX）家族的一個成員。這個基因家族的核心特征是一個新穎的，高度保守的DNA結合基序，即成對盒。成對盒轉錄因子是早期發育的重要調節因子，其基因表達的改變被認為有助于腫瘤的轉化。該基因編碼B細胞系特異性激活蛋白，在B細胞分化的早期而非晚期表達。它在中樞神經系統和睪丸的發育中也有表達，因此編碼蛋白也可能在神經發育和精子發生中發揮作用。這個基因位于9p13，它參與了T（9；14）（p13；q32）易位，在漿細胞亞型的小淋巴細胞淋巴瘤和衍生大細胞淋巴瘤中復發。這種易位使得有效的IGH基因E-MU增強子與PAX5啟動子非常接近，這表明該基因轉錄的放松調控有助于這些淋巴瘤的發病機制。選擇性剪接導致編碼不同亞型的多個轉錄變體。
This gene encodes a member of the paired box (PAX) family of transcription factors. The central feature of this gene 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 their genes are thought to contribute to neoplastic transformation. This gene 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 encoded protein may also play a role in neural development and spermatogenesis. This gene 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 this gene contributes to the pathogenesis of these lymphomas. Alternative splicing results in multiple transcript variants encoding different isoforms.