We developed a genome-wide cross-taxa approach to build a database of families of homologous sequences and to provide accurate alignments and phylogenies for the constructed families. The layout of the implementation of the PhEVER database is represented in Figure 1 and the details concerning its sequence content are available in Table 1 . In order to avoid redundancy due to the availability of numerous genomes of similar bacterial and viral strains in public databases, we collected all completely sequenced viral and bacterial genomes from RefSeq Viral (17) and Genome Reviews (18) , two non-redundant and curated databases of completely sequenced genomes. To this high-quality curated data composed of Archaea, Bacteria and Eukarya, we added nine eukaryotic genomes from Ensembl (Aedes aegypti, Anopheles gambiae, Bos taurus, Caenorhabditis elegans, Danio rerio, Drosophila melanogaster, Gallus gallus, Homo sapiens, Mus musculus) (19) to allow for a large representation of species from the different domains of life. The PhEVER database was structured under the ACNUC system (20) allowing it to be queried using a web interface and a large number of tools specifically developed for this database management system (14) .