POU domain proteins contain tow high conserved subdomains ( POU_H and POU_S) and variable linker between them. POU proteins interact with DNA by POU_H and POU_S. In aid of the domain flexibility and requirement of cofactors, POU proteins exhibit very complicated ability to bind and recognize DNA in function of regulator and transcription factors. In vertebrate and invertebrate, POU proteins take part in early embryogenesis, exert much regulation in cell lineage differentiation and neural development.