Thyrotroph embryonic factor isoform 1, also known as TEF, is a 303 amino acid nuclear transcription factor that belongs to the bZIP (basic region/leucine zipper) family and PAR (proline and acidic amino acid-rich) subfamily. TEF binds DNA as either a homodimer or heterodimer, and is known to transactivate the TSH beta promoter. TEF accumulates according to a robust circadian rhythm and has also been found to inhibit cell growth by down-regulating beta chain expression of cytokine receptors. Recombinant human TEF protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.