GADD45A, also known as growth arrest and DNA damage-inducible protein, binds both Cdks and PCNA, a protein involved in DNA replication and repair. It has been shown to stimulate DNA excision repair in vitro and to inhibit entry of cells into S phase. This protein may serve as a link between p53-dependent cell cycle checkpoint and DNA repair. Recombinant human GADD45A protein, fused to His-tag at C-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.