A new type of RefSeq accession number, of the form “NG_######”, now appears in Entrez. These accession numbers are used to designate curated genomic segments. To see all of these records in Entrez, use the query: NG_*[accn]

Examples of curated genomic regions include the human hair keratin gene cluster on chromosome 17 (NG_000018), the human alpha globin region on chromosome 16 (NG_000006), and the human MHC class III complement gene cluster on chromosome 6 (NG_000013). Such gene clusters are difficult to assemble in a purely automated fashion and are therefore maintained manually at NCBI as curated genomic segments.

Currently, all NG_ accession numbers are the result of manual curation and are thus considered to be reviewed RefSeq records. The mRNAs and proteins that these genomic segments encode are also curated and available under distinct RefSeq accession numbers with the prefixes NM_ for nucleotides and NP_ for proteins.

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