The Reference Sequence (RefSeq) database provides a biologically non-redundant collection of DNA, RNA, and protein sequences. Each RefSeq represents a single, naturally occurring molecule from a particular organism. RefSeqs are frequently based on GenBank records but differ in that each RefSeq is a synthesis of information, not a piece of a primary research data in itself. Similar to a review article in the literature, a RefSeq is an interpretation by a particular group at a particular time. RefSeqs can be retrieved in several different ways: by searching the Entrez Nucleotide or Protein database, by BLAST searching, by FTP, or through links from other NCBI resources.