The Sequence Ontology: a tool for the unification of genome annotations

Genomic annotations are the focal point of sequencing, bioinformatics analysis, and molecular biology. They are the means by which we attach what we know about a genome to its sequence. Unfortunately, biological terminology is notoriously ambiguous; the same word is often used to describe more than one thing and there are many dialects. For example, does a coding sequence (CDS) contain the stop codon or is the stop codon part of the 3'-untranslated region (3' UTR)? There really is no right or wrong answer to such questions, but consistency is crucial when attempting to compare annotations from different sources, or even when comparing annotations performed by the same group over an extended period of time.At present, GenBank [1] houses 220 viral genomes, 152 bacterial genomes, 20 eukaryotic genomes and 18 archeal genomes. Other centers such as The Institute for Genomic Research (TIGR) [2] and the Joint Genome Institute (JGI) [3] also maintain and distribute annotations, as do many model organism databases such as FlyBase [4], WormBase [5], The Arabidopsis Information Resource (TAIR) [6] and the Saccharomyces Genome Database (SGD) [7]. Each of these groups has their own databases and many use their own data model to describe their annotations. There is no single place at which all sets of genome annotations can be found, and several sets are informally mirrored in multiple locations, leading to location-specific version differences. This can make it hazardous to exchange, combine and compare annotation data. Clearly, if genomic annotations were always described using the same language, then comparative analysis of the wealth of information distributed by these institutions would be enormously simplified: Hence the Sequence Ontology (SO) project. SO began 2 years ago, when a group of scientists and developers from the model organism databases - FlyBase, WormBase, Ensembl, SGD and MGI - came together to collect and unify the terms they used in their sequence annotation