CTDSPL, also known as CTD small phosphatase-like protein, preferentially catalyzes the dephosphorylation of 'Ser-5' within the tandem 7 residues repeats in the C-terminal domain (CTD) of the largest RNA polymerase II subunit POLR2A. Recombinant human CTDSPL protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography.