TCEA1 (Transcription elongation factor A protein 1) belongs to the TFS-II family. TCEA1 binds to Pol II and functions to cleave the nascent transcript, thereby unlocking the complex and allowing transcription to continue. Localized to the nucleus, TCEA1 contains three independently-folding domains, all of which are necessary for proper binding to Pol II. The arresting sites in DNA have the property of trapping a certain fraction of elongating RNA polymerases that pass through, resulting in locked ternary complexes. Cleavage of the nascent transcript by S-II allows the resumption of elongation from the new 3'-terminus. Recombinant human TCEA1 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.