The Tudor domain is a domain of around 50-70 amino acids which was first identified as a repeat present in 10 copies in Drosophila Tudor protein [1,2]. The Tudor domain is found in one or several copies in many eukaryotic proteins that colocalize with ribonucleoprotein or single-stranded DNA-associated complexes in the nucleus, in the mitochondrial membrane, or at kinetochores. The Tudor domain can be found in association with other domains, such as a staphylococcal nuclease (SN)-fold (see <PDOC00865>), a OTU domain (see <PDOC50802>), a KH domain (see <PDOC50084>), a DEAD/DEAH box helicase domain (see <PDOC00039>) or a coiled-coil domain. An insufficient amount of functional information concerning the proteins containing a Tudor domain is currently available from which to ascribe putative functions to Tudor domains. However, it is likely that Tudor domains function as protein-protein interaction motifs during RNA metabolism and/or transport and do not bind to RNA directly [1,3,4].

The resolution of the solution structure of the Tudor domain of human SMN revealed that the Tudor domain forms a strongly bent antiparallel β-sheet with five strands forming a barrel-like fold. The structure exhibits a conserved negatively charged surface that interacts with the C-terminal Arg and Gly-rich tails of the spliceosomal Sm D1 and D3 proteins [4].

Some proteins known to contain a Tudor domain are listed below:

• Drosophila Tudor, a protein required during oogenesis for the formation of primordial germ cells and for normal abdominal segmentation.
• Drosophila Homeless (HLS), a protein belonging to the DE-H family of RNA- dependent ATPases that is required for RNA localization during oogenesis. HLS might function during the processing of pre-mRNA whose products direct microtubules organization, which is required for mRNA transport.
• Drosophila ovarian tumor protein (OTU). OTU is required at multiple stages of oogenesis and the Tudor domain is required for its early function. A portion of OTU cofractionates with mRNA/protein complexes (mRNPs) [5].
• Mammalian survival of motor neuron protein (SMN). SMN participates in small nuclear ribonucleoprotein (snRNP) particles assembly in the cytoplasm and may also affect splicing more directly in the nucleus. In human, defects of the SMN protein are associated with spinal muscular atrophy (SMA), a disease in which the anterior horn cells in the spinal corn die, resulting in progressive muscle weakness and ultimately, in some cases, in the inability to breathe and swallow.
• Human A-kinase anchor protein 1 (AKAP1). It binds to type I and II regulatory subunits of protein kinase a and anchors them to the cytoplasmic face of the mitochondrial outer membrane. An alternatively spliced version of AKAP1 (S-AKAP84) participates in spermiogenesis, probably by facilitating ordering of spermatid mitochondria.
• Human p100, a nuclear protein that coactivates gene expression mediated by the Epstein-Barr virus nuclear antigen 2 (EBNA-2). The p100 protein is also able to bind single-stranded DNA.
• Human Tudor and KH domain-containing protein (TDRKH) [6].
• Rat Tudor repeat associator with PCTAIRE 2 (Trap). Trap contains five Tudor domains and interacts with the N-terminal domain of PCTAIRE 1 and 2, members of Cdk-related kinases which is highly expressed in the nervous system.
• Caenorhabditis elegans hypothetical protein C56G2.1.
• Rice Rp120, a protein that binds to a wide range of mRNAs expressed during seed development and is associated with the cytoskeleton [7].

The profile we developed covers the entire Tudor domain.