AICDA, also known as AID, is involved in somatic hypermutation, gene conversion, and class-switch recombination in B-lymphocytes. This protein is required for several crucial steps of B-cell terminal differentiation necessary for efficient antibody responses. It may also play a role in the epigenetic regulation of gene expression by participating in DNA demethylation. Recombinant human AICDA protein, fused to His-tag at N-terminus, was expressed in E.coli.