POU domain, class 5, transcription factor 1, also known as OCT4, binds to the octamer motif (5'-ATTTGCAT-3'). This protein forms a trimeric complex with SOX2 on DNA and controls the expression of a number of genes involved in embryonic development such as YES1, FGF4, UTF1 and ZFP206. It is critical for early embryogenesis and for embryonic stem cell pluripotency. Recombinant human OCT4 protein, fused to His-tag at N-terminus, was expressed in E.coli.