Entrez (11) is an integrated database retrieval system that provides access to a diverse set of 38 databases that together contain over 400 million records (Table 1). Entrez supports text searching using simple Boolean queries, downloading of data in various formats and linking of records between databases based on biological relationships. In their simplest form, these links may be cross-references between a sequence and the abstract of the paper in which it is reported, or between a protein sequence and its coding DNA sequence or its 3D structure. Computationally derived links between ‘neighboring records’, such as those based on computed similarities among sequences or among PubMed abstracts, allow rapid access to groups of related records. A service called LinkOut expands the range of links to include external services, such as organism-specific genome databases. The records retrieved in Entrez can be displayed in many formats and downloaded singly or in batches. Table 1.The Entrez Databases (as of 8/14/2009)DatabaseRecordsSection within this articleNucleotide78 783 103Genes and Associated SequencesEST62 838 170Genes and Associated SequencesPubChem Substance61 056 228Small Molecules and BioassaysSNP59 806 469Genotypes and PhenotypesGEO
