POU domain


POU is a family of eukaryotic transcription factors that have well-conserved homeodomains. The Pou domain is a bipartite DNA binding domain found in these proteins.

Etymology

The acronym POU is derived from the names of three transcription
factors:
POU domain genes have been described in organisms as divergent as
Caenorhabditis elegans, Drosophila, Xenopus,
zebrafish and human but have not been yet identified in plants
and fungi.
Comparisons of POU domain genes across the animals suggests that the family can be divided into six major classes. Pit-1 is part of the POU1 class, Oct-1 and Oct-2 are members of POU2, while Unc-86 is a member of POU4. The six classes diverged early in animal evolution: POU1, POU3, POU4, and POU6 classes evolved before the last common ancestor of sponges and eumetazoans, POU2 evolved in the Bilatera, and POU5 appears to be unique to vertebrates.
There is a surprisingly high degree of amino acid sequence conservation
of POU homeodomains to the transcriptional regulator comS, the competence protein from the gram positive prokaryote Bacillus subtilis. Akin to the way that POU homeodomain
regulators lead to tissue differentiation in metazoans, this
transcription factor is critical for differentiation of a subpopulation
of B. subtilis into a state of genetic competence.

Function

POU proteins are eukaryotic transcription factors containing a bipartite DNA binding domain referred to as the POU domain. The various members of the POU family have a wide variety of functions, all of which are related to the function of the neuroendocrine system and the development of an organism. Some other genes are also regulated, including those for immunoglobulin light and heavy chains, and trophic hormone genes, such as
those for prolactin and growth hormone.

Structure

The POU domain is a bipartite domain composed of two subunits separated by a non-conserved region of 15-55 aa. The N-terminal subunit is known as the POU-specific domain, while the C-terminal subunit is a homeobox domain. 3D structures of complexes including both POU subdomains bound to DNA are available. Both subdomains contain the structural motif 'helix-turn-helix', which directly associates with the two components of bipartite DNA binding sites, and both are required for high affinity sequence-specific DNA-binding. The domain may also be involved in protein-protein interactions. The subdomains are connected by a flexible linker. In proteins a POU-specific domain is always accompanied by a homeodomain. Despite the lack of sequence homology, 3D structure of POUs is similar to 3D structure of bacteriophage lambda repressor and other members of HTH_3 family.

Examples

Human genes encoding proteins containing the POU domain and related pseudogenes include: