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October 18, 2006 [posted]

RefSeq Accession Numbers in MEDLINE®

accession numbers for the Reference Sequence (RefSeq) collection are now being added to MEDLINE records when a journal article reports that new data has been added to that database. RefSeq is a collection of authoritative sequences for important model organisms. Included are genomic DNA, transcript (RNA), and protein products. RefSeq was developed and is maintained by the National Center for Biotechnology (NCBI) and additional information is available at: //

Every RefSeq record is assigned an accession number that has a standard format. The format consists of a two-letter prefix, followed by an underscore, followed by a six- or nine-character number. At this time, the prefixes are: AC, AP, NC, NG, NM, NP, NR, NT, NW, NZ, XM, XP, XR, YP or ZP. For more on the accession number format go to //

In PubMed®, RefSeq accession numbers display in the Secondary Source ID (SI) field in the Citation and MEDLINE display formats and in the <DataBankList> area of the XML format. An example as it appears in the Citation display is:

Secondary Source ID:
  • RefSeq/NP_565616

RefSeq numbers may be searched in PubMed using the [si] search tag.

  1. To retrieve a specific accession number:
    refseq/np_565616 [si]
    np_565616 [si]
    Click on the number's link in the Citation display (e.g., RefSeq/NP_565616) to see search links for PubMed and Nucleotide or Protein databases.
  2. To retrieve all PubMed records with RefSeq accession numbers:
    refseq [si]

NLM® began to include RefSeq accession numbers in citations that have undergone data quality review after September 28, 2006 and when those numbers appear at the beginning or end of an article where other databank and grant information is found. NLM plans to edit some older citations as well to add RefSeq numbers.

By Andrea Demsey
MEDLARS Management Section

Demsey A. RefSeq Accession Numbers in MEDLINE®. NLM Tech Bull. 2006 Sep-Oct;(352):e7.

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